necessary

14.0.8 • Public • Published

Necessary

A collection of utility functions.

This package was partly inspired by lodash, async and the like. The idea was to create utility functions that addressed some modest requirements and would result in a relatively small footprint. That said, the bare bones implementations, especially the asynchronous functions, should provide some confidence whilst debugging.

These can only be used in the browser:

These cna only be used on Node:

These can be used both on Node and in the browser:

Installation

You can install Necessary with npm:

npm install necessary

You can also clone the repository with Git...

git clone https://github.com/djalbat/necessary.git

...and then install the dependencies with npm from within the project's root directory:

npm install

Usage

Each of the collections of utility functions described below is exported as a plain old JavaScript object. To get hold of them, import the requisite object and then destructure it:

import { arrayUtilities, asynchronousUtilities, fileSystemUtilities } from "necessary";

const { first, last } = arrayUtilities,
      { isDirectory } = fileSystemUtilities;

...

Or the require() function can be used where appropriate:

const { arrayUtilities, asynchronousUtilities, fileSystemUtilities } = require("necessary");

const { first, last } = arrayUtilities,
      { isDirectory } = fileSystemUtilities;

...

The miscellaneous functions are a special case. They can be treated as above but may well have other functions assigned to them. See below.

Ajax utilities

  • get()
  • post()cp
  • request()

The first two get() and post() functions make use of the third request() function, which is more generic and can be used for arbitrary HTTP requests.

  • The get() function sends a GET request, taking host, uri, query and operation arguments, together with an optional headers argument after the query argument.

The query argument should be a plain old JavaScript object, the names and values of which are encoded and concatenated to form the query string.

The headers argument should also be a plain old JavaScript object. If it does not have an accept property then one wil be provided with the value application/json.

The callback argument is expected to be a function taking content and statusCode arguments. If the accept property of the main headers argument is set to application/json then the operation's content argument can be assumed to be JSON, or null if the request body cannot be parsed as such. The statusCode argument will be the response status code, for example 200 for a successful OK response.

const host = "...",
      uri = "...",
      query = {
        ...
      };

get(host, uri, query, (json, statusCode) => {
  if (statusCode === 200) {
    ...
  }
});

Note that the uri argument must include a leading forward slash / since the host argument should not have a trailing one.

  • The post() function behaves almost identically to the get() function, with the following differences.

It sends a POST rather than a GET request. There is an additional content argument that comes before the callabck argument and after the headers argument, which is again optional. If the headers argument does not have a content-type property then one will be provided with the value of application/json. If the content-type property of the headers argument is set to application/json then the content argument is assumed to be a plain old JavaScript object and is stringified as JSON.

const host = "...",
      uri = "...",
      query = {
        ...
      },
      json = {
        ...
      };

post(host, uri, query, json, (json, statusCode) => {
  if (json !== null) {
    ...
  }
});
  • The request() function behaves similarly to the post() function but the headers argument is no longer optional and there is a method argument that comes before the content argument:
const host = "...",
      uri = "...",
      query = {
        ...
      },
      method = "PUT"
      headers = {
        "accept": "application/json",
        "content-type": "application/json"
      },
      json = {
        ...
      };

request(host, uri, query, method, headers, json, (json, statusCode) => {
  if (json !== null) {
    ...
  }
});

Note that the headers argument is not optional this time.

Shell utilities

  • prompt()

Functions for applications running on a shell such as Bash or ZSH. In fact there is only one currently.

  • The prompt() function is meant for use in shell applications. It takes a plain old JavaScript options object and a callback function as its first and second arguments, respectively:
const hidden = true,
      answer = ...,
      description = ...,
      errorMessage = ...,
      validationFunction = ...,
      options = {
        hidden,
        answer,
        description,
        errorMessage,
        validationFunction
      };

prompt(options, (answer) => {
  ...
});

There are a range of properties available for the options object. The description and errorMessage properties are mandatory. The remaining properties are optional.

The default values of the attempts and encoding properties are 3 and utf8, respectively. The default value of the hidden property is false. Setting it to true results in password-style input, that is, the characters remain hidden.

If no validateFunction property is given then you must set a validatePattern property instead, which must be a regular expression.

The initialAnswer property sets the initial answer at the prompt. You might want to set it to yes, for example. Lastly, setting the answer property to anything other than null or undefined causes the callback function to be invoked immediately without any prompt being shown. This can be useful for debugging.

Logging utilities

  • log()

A single log() function for basic logging purposes.

  • The log() function provides rudimentary logging functionality, printing its argument to the console, prepended with a date and time stamp together with the path of the file containing the callee function and the line number:
log("...") // Results in '28-01-2018 15:44:47.363 bin/main.js(35) ...' being logged.

You can pass an error instead of a string to log(), in which case it will print the file path and line number of the place where the error was thrown along with the error message.

Additionally, it is possible to print to a log file if a log directory and, optionally, a base name for the log file are specified. The base name here means the file name minus the extension and separator. The default is default:

const { setLogFileBaseName, setLogDirectoryPath } = log;

setLogFileBaseName("example");
setLogDirectoryPath("./log");

log("...") // Results in '28-01-2018 15:44:47.363 bin/main.js(35) ...\n' line being appended to
           // the './log/example.log' file as well as the message being logged.

A standard set of functions, namely fatal(), error(), warning(), info(), debug() and trace(), are available and these are filtered in the usual way, assuming the log level has been set:

const { setLogLevel, DEBUG } = log;

setLogLevel(DEBUG);

log.error("...") // Printed to the console and optionally, to the log file.
log.trace("...") // Ignored, because the trace level is lower than the debug level.

There is also a setLogOptions() function which allows you to pass the log level, base file name and directory path as a plain old JavaScript object. See below for a usage example.

Finally, log files are rolled over every night. So ./log/example.log would become ./log/example.28-01-2018.log and a new ./log/example.log file would be started at midnight.

Request utilities

  • createRequest()
  • createGetRequest()
  • createPostRequest()

Functions that leverage Node's HTTP nad HTTPS inbuilt modules in order to provide HTTP request functionality. These functions are deliberately low level. They will take away some of the pain of using the aforementioned modules but will not automatically set headers, parse responses, etc. Specifically, methods have to be called on the instance of the ClientRequest class that they each return in order to make the request and on the instance of the IncomingMessage passed to the callback function in order to parse the response.

  • The createRequest() function provides a means to make arbitrary requests. It takes host, uri, query, method, headers and callback arguments. It returns an instance of Node's ClientRequest class. The callback function must have an error argument, which will be null if the request is successful, and a response argument, which will be an instance of Node's IncomingMessage class. The query and headers arguments should be plain old JavaScript objects, with the former being converted into a query string. The other arguments bar the last callback argument should be strings.

In the following example a GET request is made. Note that because the request body is empty, it is enough to call the request object's end() method in order to make the request. Note also that the response is piped directly to a file.

const { createWriteStream } = require("fs");

const host = ...,
      uri = ...,
      query = {
        ...
      },
      method = "GET",
      headers = {
        ...
      },
      request = createRequest(host, uri, query, method, headers, (error, response) => {
        ...

        const writeStream = createWriteStream(...);

        response.pipe(writeStream);
      });

request.end();

In the following example the queryStringFromQuery() function from the HTTP utilities is used to encode the body of the request. Note that the content-type header is set explicitly. Note that the request body is piped directly from a file:

const { createReadStream } = require("fs");

const host = ...,
      uri = ...,
      query = {},
      method = "POST",
      headers = {
        "content-type": "image/png"
      },
      request = createRequest(host, uri, query, method, headers, (error, response) => {
        ...
      }),
      readStream = createReadStream(...);

readStream.pipe(request);

Finally, in the following example a contentFromResponse() function has been written in order to parse the response to a string in preference to piping it to a file, say:

const host = ...,
      uri = ...,
      query = {
        ...
      },
      method = "GET",
      headers = {
        ...
      },
      request = createRequest(host, uri, query, method, headers, (error, response) => {
        contentFromResponse(response, (content) => {
          console.log(content)
        });
      });

request.end();

function contentFromResponse(response, callback) {
  let content = "";

  response.on("data", (data) => {
    content += data;
  });

  response.on("end", () => {
    callback(content);
  });
}
  • The createGetRequest() function is identical to the createRequest() function except that the method argument is omitted and the headers argument is optional.

  • The createPostRequest() function is identical to the createRequest() function except that the method argument is omitted and the headers argument is optional.

Package utilities

  • getName()
  • getAuthor()
  • getVersion()
  • getLicense()
  • getPackagePath()
  • getPackageJSON()

A getPackageJSON() function for retrieving the contents of the package.json file together with a few helper functions to retrieve the more common entries and a packagePath() function that returns the package's path.

  • The getName(), getAuthor(), getVersion() and getLicense() functions return the value of the requisite entries in the package.json file.
const version = getVersion(); // Returns the package version.

From here the package's JSON can be destructured to recover specific entries not covered by the above helper functions.

  • The getPackagePath() function returns the path of the package, that is, the full path of the directory that contains the package in any node_modules directory.
const packagePath = getPackagePath(); // Returns the package's path.
  • The getPackageJSON() function returns the contents of pakcage.json file in JSON form.
const packageJSON = getPackageJSON(); // Returns the contents of the package.json file.

Template utilities

  • parseFile()
  • parseContent()
  • parseLine()

These functions parse files, content or single lines, replacing each token of the form ${<name>} with the value of the corresponding property of a plain old JavaScript object passed as the second argument, or replacing the token with an empty string if no such property exists.

  • The parseFile() function takes a file path as the first argument:
const filePath = "/etc/var/public/name.html",
      name = "Joe Bloggs",
      age = 99,
      args = {
        name,
        age
      }
      parsedContent = parseFile(filePath, args);
  • The parseContent() function takes content as the first argument, honouring newline \n characters:
const content = `

  name: <strong>${name}</strong><br/>
  age: <strong>${age}</strong><br/>

      `,
      name = "Joe Bloggs",
      age = 99,
      args = {
        name,
        age
      }
      parsedContent = parseContent(content, args);
  • The parseLine() function takes a single line of content as the first argument:
const line = "${name}, aged ${age}.",
      name = "Joe Bloggs",
      age = 99,
      args = {
        name,
        age
      }
      parsedLine = parseLine(line, args); // returns 'Joe Bloggs, aged 99.'

File system utilities

  • getEntryStats()
  • checkEntryExists()
  • checkFileExists()
  • checkDirectoryExists()
  • isEntryFile()
  • isEntryDirectory()
  • isDirectoryEmpty()
  • readDirectory()
  • readFile()
  • copyFile()
  • writeFile()
  • appendToFile()
  • createDirectory()
  • createFile()
  • moveEntry()
  • renameEntry()
  • removeEntry()

An inglorious collection of functions which do no more than paper over some of Node's synchronous native file system API functions. All of the functions will throw native errors upon failure.

  • The getEntryStats() function returns an instance of the fs.Stats class:
const stats = getStats("root/etc"); // returns stats for the 'root/etc' entry
  • The checkEntryExists(), checkFileExists(), checkDirectoryExists(), isEntryFile(), isEntryDirectory() and isDirectoryEmpty() functions work as their names suggest, returning a boolean value.
checkEntryExists("root/etc"); // returns true if the file or directory exists

checkFileExists("root/etc/init.conf"); // returns true if the file exists

checkDirectoryExists("root/etcconf"); // returns true if the directory exists

isEntryFile("root/etc/init.conf"); // returns true if the entry is a file

isEntryDirectory("root"); // returns true if the entry is a directory

isDirectoryEmpty("root/etc"); // returns true if the directory is empty
  • The readDirectory() function returns an array of entry names if the directory exists:
readDirectory("root/etc"); // returns the contents of the 'root/etc' directory
  • The readFile() function takes the file encoding as an optional second string argument. The default is utf8. It returns the content of the file upon success:
readFile("root/etc/init.conf"); // returns the content of the 'root/etc/init.conf' file
  • The copyFile() function takes as arguments the source and target file paths. It will overwrite an existing file without throwing an error. It does not return anything upon success:
copyFile("root/etc/init.conf", "tmp/init.conf"); // copies the 'init.conf' file in the '/root/etc' folder to the '/tmp' folder
  • The writeFile() function takes the content of the file as a second string argument. It does not return anything upon success:
writeFile("root/etc/init.conf", ""); // writes '' to the 'root/etc/init.conf' file
  • The appendToFile() function takes the content to append file as a second string argument. It will create teh file if necessary and does not return anything upon success:
appendToFile("root/etc/init.conf", ""); // appends '' to the 'root/etc/init.conf' file
  • The createDirectory() function creates a directory, also creating the parent directories if necessary:
createDirectory("root/etc/init"); // Creates the 'root/etc/init' directory
  • The createFile() creates an empty file. It does not return anything upon success:
createFile("root/etc/init.conf"); // writes '' to the 'root/etc/init.conf' file
  • The moveEntry() function moves a file or directory:
moveEntry("/root/usr", "/etc/lib"); // Moves the '/root/usr' directory to '/etc/lib'
  • The removeEntry() function removes a file or directory:
removeEntry("/root/etc/init"); // Removes the '/root/etc/init' directory and all of its sub-entries

Note that in the case of a directory, all of its sub-entries will be removed as well.

  • The renameEntry() function renames a file or directory:
renameFile("hosts", "host"); // Renames the 'hosts' file to 'host'

Note that if the parent directory of the newly named file or directory does not exist then this function will fail. Instead use the moveEntry() function.

Configuration utilities

  • rc()

A single rc() function for runtime configuration.

  • The rc() function parses a JSON runtime configuration file of a certain format and provides the information therein by assigning it to itself. For example:
rc();

const { logOptions } = rc;

setLogOptions(logOptions);

The default name for the file is .rc and it must be present in the current working directory. It must have the following format:

{
  "environments": [
    {
      "name": "development",
      ...
    },
    {
      "name": "production",
      ...
    }
  ]
}

If an environment name is not passed as the rc() function's argument then it will try to find the environment name by the following means:

  1. Checking the process.argv array for an --environment argument.
  2. Checking the proxess.env object for an ENVIRONMENT environment variable.

If neither of these checks are successful then it will return the first element of the enviromnents array.

Note that it will not try to assign the name property of the chosen environment to itself, because functions already have a name property.

Before returning the JSON, it will search for uppercase strings. If such a string is the name of an environment variable, it will be replaced by the environment variable's value. This means that you can choose to keep sensitive information out of the runtime configuration and therefore, for instance, safely commit it to the repository.

You can change the base extension of the file that is parsed, that is the part of the extension between the leading dot and rc, by making use of the setRCBaseExtension() function:

const { setRCBaseExtension } = rc;

setRCBaseExtension("default");

rc(); // Provides the first environment in the '.defaultrc' file

Note that the rc() function can be included in any file but only needs to be called once. But be careful that it is called before it is ever destructured.

Aside from the aforementioned setRCBaseExtension() functions, the checkRCFileExists(), createVacuousRCFile(), readRCFile() and writeRCFile() functions do as their names suggest. The updateRCFile() function, if passed a plain old JavaScript object as the first argument, will add the properties therein, overwriting any existing properties. Properties to be removed can be given as further arguments. If you do not want to add as well as remove properties, set the first argument to a falsey value.

const { readRCFile, writeRCFile, updateRCFile, checkRCFileExists, createVacuousRCFile } = rc;

const rcFileExists = checkRCFileExists();  // Returns true if the rc file exists.

createVacuousRCFile(); // creates an rc file with an empty environment.

const json = readRCFile();  // Reads the entire contents of the rc file into a JSON object

writeRCFile(json);  // Stringifies the given JSON object and writes it to the rc file

updateRCFile({example: "example"});  // Updates the rc file, adding the 'example' property

updateRCFile(null, "example");  // Updates the rc file, removing the 'example' property

Path utilities

  • isPathName()
  • isPathTopmostName()
  • isPathRelativePath()
  • isPathAbsolutePath()
  • isTopmostNameInAbsolutePath()
  • combinePaths()
  • concatenatePaths()
  • bottommostNameFromPath()
  • topmostDirectoryPathFromPath()
  • topmostDirectoryNameFromPath()
  • pathWithoutBottommostNameFromPath()
  • pathWithoutTopmostDirectoryNameFromPath()

These functions manipulate or query strings that represent file and directory paths. Note that only forward slash / delimiters are supported. Trailing delimiters are not needed, but tolerated.

  • The isPathName() function returns true if the string argument contains no / delimiters apart from the first and last characters:
isPathName("root/"); // returns true

isPathName("/root"); // returns true

isPathName("./root"); // returns false

isPathName("../etc"); // returns false

isPathName("/root/etc"); // returns false
  • The isPathTopmostName() function returns true if the string argument is both a name and an absolute path:
isPathTopmostName("/root/"); // returns true

isPathTopmostName("/root"); // returns true

isPathTopmostName("etc/"); // returns false
  • The isPathRelativePath() function returns true if the string argument does not start with a delimiter/:
isPathRelativePath("etc"); // returns true

isPathRelativePath("./etc"); // returns true

isPathRelativePath("../etc"); // returns true
  • The isPathAbsolutePath() returns true if the string argument starts with a delimiter/:
isPathAbsolutePath("/root/etc"); // returns true
  • The isTopmostNameInAbsolutePath() function returns true if the second string argument begins with the first string argument optionally followed by a delimiter/ and further characters:
isTopmostNameInAbsolutePath("/root", "/root/etc");  // returns true

isTopmostNameInAbsolutePath("root", "/root/etc");  // returns false

isTopmostNameInAbsolutePath("etc", "/root/etc"); // returns false

Note that the function assumes that the first argument is a topmost name and that the second argument is an abolute path. It does not check, it simply compares the two arguments with a single regex.

  • The combinePaths() function will combine the first string argument with the second string argument by successively removing the bottommost directory name of the former for each topmost parent directory .. signifier it finds in the latter. Current directory . signifiers are also removed:
combinePaths("etc/", "./init"); // returns 'etc/init'

combinePaths("/root/etc/", "../init"); // returns '/root/init'

Note that the function assumes that the second argument is a relative name or path.

  • The concatenatePaths() function will concatenate the first and second string arguments, adding the trailing forward slash / to the first string if necessary:
concatenatePaths("root", "etc/"); // returns 'root/etc/'

concatenatePaths("root/", "etc/"); // returns 'root/etc/'

Note that the function assumes that the second argument is a relative name or path although without a leading current directory . or parent directory .. signifier.

  • The bottommostNameFromPath(), topmostDirectoryPathFromPath(), topmostDirectoryNameFromPath(), pathWithoutBottommostNameFromPath() and pathWithoutTopmostDirectoryNameFromPath() functions work as their names suggest. Each expects there to be at least one delimiter, returning null otherwise:
bottommostNameFromPath("../etc"); // returns 'etc'

topmostDirectoryPathFromPath("/root/etc/init.conf"); // returns '/root/etc'

topmostDirectoryNameFromPath("etc/init.conf"); // returns 'etc'

pathWithoutBottommostNameFromPath("root/etc/init.conf"); // returns 'root/etc'

pathWithoutTopmostDirectoryNameFromPath("root/etc/init.conf"); // returns 'etc/init.conf'

Array utilities

  • first()
  • second()
  • third()
  • fourth()
  • fifth()
  • sixth()
  • seventh()
  • eighth()
  • ninth()
  • firstLast()
  • secondLast()
  • thirdLast()
  • fourthLast()
  • fifthLast()
  • sixthLast()
  • seventhLast()
  • eighthLast()
  • ninthLast()
  • last()
  • head()
  • tail()
  • back()
  • front()
  • push()
  • unshift()
  • concat()
  • clear()
  • copy()
  • merge()
  • match()
  • find()
  • replace()
  • splice()
  • filter()
  • prune()
  • extract()
  • patch()
  • compress()
  • combine()
  • augment()
  • separate()
  • forwardsFind()
  • backwardsFind()
  • forwardsSome()
  • backwardsSome()
  • forwardsEvery()
  • backwardsEvery()
  • forwardsReduce()
  • backwardsReduce()
  • forwardsForEach()
  • backwardsForEach()

Note that none of these functions take or pass on a thisArg argument when they might otherwise have done. Use bind().

  • The functions first() through to last() return the requisite element of the array argument, if passed an array of at least the required length. If the array is not long enough they return undefined.

  • The head() function returns an array containing the first element of its array argument whilst the tail() function returns an array containing all but the first element of its array argument. The back() function returns an array containing hte last element of its array argument whilst the front() function returns an array returning all but the last element of its array argument.

  • The push() function is similar to its native counterpart but will push an array rather than a single element.

  • The unshift() function is similar to its native counterpart but will unshift an array rather than a single element.

  • The concat() function is similar to its native counterpart, however it alters the first array argument in place. Like its native counterpart it will also take a single element as the second argument and convert it to an array.

concat([1, 2, 3], 4); // the array argument becomes [1, 2, 3, 4]
  • The clear() function removes all the elements in the array argument and returns them as a fresh array:
clear([1, 2, 3]); // the array argument becomes []
  • The copy() function copies the second array argument over the top of the first array argument, in other words it replaces each element of the first array argument with the corresponding element in the second array argument. If there are more elements in the second array argument that the first, the first is lengthened:
copy([1, 2, 3], [4, 5, 6, 7]); // the first array argument becomes [4, 5, 6, 7]
  • The merge() function copies the second array argument onto to the end of the first array argument, behaving in identical fashion to the push() function:
merge([1, 2, 3], [4, 5, 6, 7]); // the first array argument becomes [1, 2, 3, 4, 5, 6, 7]
  • The match() function compares the first and second array arguments. If they are of the same length and the callback argument supplied returns a truthy value when invoked with each pair of elements then it returns true:
match([1, 2, 3], [-1, -2, -3], (valueA, valueB) => (valueA === -valueB)); // returns true
  • The find() function is like its native counterpart, however it returns an array of all the elements for which the callback function returns a truthy value, rather than just the first:
find([1, 2, -1, -2], (element, index) => (element > 0)); // returns [1, 2]
  • The replace() function will replace an element in the array with the given element the first time that the callback function returns a truthy value:
replace([1, 0, -2], 3, (element, index) => (element === 0)); // the array argument becomes [1, 3, -2]
  • The splice() function works in a similar vein to its native counterpart, however it takes an array as the optional fourth argument rather than a series of elements from the fourth argument onwards. It mutates the first array argument and returns an array of the elements that have been deleted:
splice([1, 2, 3], 1, 2, [4, 5]); // the first array argument becomes [1, 4, 5]
  • The filter() function is like its native counterpart, however it filters the first array argument in place. The second argument should be a callback function that will be invoked for each element of the array. If it does not return a truthy value, the corresponding element will be deleted. The deleted elements are returned.
filter([1, 2, -2], (element, index) => (element > 0)); // returns [-2] and the array argument becomes [1, 2] 
  • The prune() function is much like the filter() function, however it will terminate the first time that the callback function does not return a truthy value:
prune([1, 2, -1, -2], (element, index) => (element > 0)); // returns -1 and the array argument becomes [1, 2, -2]
  • The extract() function is identical to the prune() function, however the callback should return a truthy value in order to delete and return an element:
extract([1, 2, -1, -2], (element, index) => (element === 2)); // returns 2 and the array argument becomes [1, -1, -2]
  • The patch() function will append the given element to the array argument the first time that the callback function returns a truthy value:
patch([1, 2, 0, -1, -2], 4, (element, index) => (element === 0)); // the array argument becomes [1, 2, 0, -1, -2, 4]
  • The compress() function will remove elements from the array argument whenever the callback function returns a truthy value:
compress([1, 2, 1], (element1, element2) => (element1 === element2)); // the array argument becomes [1, 2]
  • The combine() function will concatenate the two array arguments, combine them and and return the result
combine([1, 2, 1], [2, 3], (element1, element2) => (element1 === element2)); // returns [1, 2, 3]
  • The augment() function appends each of the elements of the second array argument to the first array argument whenever the callback returns a truthy value:
augment([1, 2, 3], [-1, 4, -2, 5], (element, index) => (element > 0)); // the array argument becomes [1, 2, 3, 4, 5]
  • The separate() function separates the first array argument, pushing each of its elements onto either the second or the third array argument depending on whether or not the callback returns a truthy value:
separate([1, -1, -2, 2, 3, -3], [], [], (element, index) => {(element > 0)); // the second and third array arguments become [1, 2, 3] and [-1, -2, 3], respectively.

The forwardsXXX() and backwardsXXX()functions do as their names suggest. The fowardsXXX() function take an array for their first argument but otherwise behave identically to their native counterparts. The backwardsXXX() functions behave similarly, only backwards.

HTTP utilities

  • overwrite()
  • underwrite()
  • portFromHost()
  • secureFromHost()
  • hostnameFromHost()
  • queryStringFromQuery()
  • urlFromHostURIAndQuery()

Helper functions to manipulate HTTP headers and URLs, build query strings and so on.

  • The overwrite() function takes a plain old JavaScript object headers argument together with name and value string arguments. If the corresponding property of the headers object exists then it is replaced with the value value. This function's utility lies in the fact that the name comparisons are case insensitive.
const headers = {
  "Content-Type": "application/json"
};

overwrite(headers, "content-type", "text/html"); // headers["Content-Type"] = "text/html"
  • The underwrite() function takes a plain old JavaScript object headers argument together with name and value string arguments. If the corresponding property of the headers object does not exist then it is created with the value value. This function's utility lies in the fact that the name comparisons are case insensitive.
const headers = {
  "Content-Type": "application/json"
};

underwrite(headers, "content-type", "text/html"); // headers["Content-Type"] = "application/jon"

const headers = {};

underwrite(headers, "content-type", "text/html"); // headers["content-type"] = "text/html"
  • The portFromHost() extracts the port from the host argument if it is specified explicitly otherwise it returns 443 for secure hosts, 80 otherwise.
portFromHost("http://site.com"); // returns 80

portFromHost("https://site.com"); // returns 443

portFromHost("http://localhost:8080"); // returns 8080
  • The secureFromHost() returns true if the protocol of the given host argument is https://, false otherwise.
secureFromHost("http://localhost"); // returns false

secureFromHost("https://site.com"); // returns true
  • The hostnameFromHost() returns the hostname part of the host argument, removing the protocol but leaving the port if present.
hostnameFromHost("http://site.com"); // returns "site.com"
  • The queryStringFromQuery() function takes a plain old JavaScript object query argument and returns the corresponding URL encoded query string. It uses the encodeURIComponent to encode the names and values
const query = {
  "name": "John Doe"
};

queryStringFromQuery(query); // returns John%20Doe
  • The urlFromHostURIAndQuery() function takes host and uri string arguments together with a query plain old JavaScript object argument. It creates a query string from the query object and concatenates this with the two other arguments in oder to create a fully qualified HTTP URL.
const host = "https://site.com",
      uri = "/user",
      query = {
        "name": "John Doe"
      };

urlFromHostURIAndQuery(host, uri, query); // returns "https://site.com/user?name=John%20Doe"

Ideally the host argument should not include a trailing forward slash whereas uri arguments should always start with a leading forward slash.

String utilities

  • strlen()
  • strcmp()
  • indexOf()
  • substring()

String functions with support for Unicode. Specifically, characters in Unicode astral plains are counted twice in native string functions and methods whereas these functions effectively count astral Unicode characters only once.

  • The strlen() function takes a single string argument. It works in much the same way as the length property of the String prototype, however it is Unicode safe:
"𝔸𝔹C".length = 5  // The 𝔹 and C characters are in an astral plane and count as two each.

strlen("𝔸𝔹C") = 3 // The string is converted to an array whose length is 3.

  • The strcmp function takes stringA and stringB arguments. It compares them character by character in order to find the lexicographically lesser of the two. Its return value is the difference between the code points of the first differing characters, with the code point of either string given as zero if it is empty. Some examples should clarify:
strcmp("", "") = 0;

strcmp("a", "") < 0;

strcmp("", "a") > 0;

strcmp("a", "a") = 0;

strcmp("ab", "a") < 0;

strcmp("ab", "ac") > 0;

strcmp("C", "𝔸") > 0;

Note that, conceptually speaking, the first argument is taken away from the second argument in order to compute the difference and not the other way around.

Note also that the double-struck C is in the basic multilingual plane and has code point 0x02102 whereas the double-struck 𝔸 is in an astral plane and has code point 0x1D538, therefore their difference is positive.

  • The indexOf() function takes string and searchString and works in identical fashion to the String class' indexOf() method, however it is Unicode safe:
indexOf("𝔸b", "b"); // Returns 1. 

In the above example the aforementioned native method would return 2.

  • The substring() function takes string and start arguments and an optional end argument. It works in much the same way as the substring() method of the String prototype, however it is Unicode safe:
"𝔸𝔹C".substring(3) = "C" // The 𝔹 character is in an astral plane and counts as two.  

substring("𝔸𝔹C", 2) = "C" // Again the string is converted to an array and thus the third character is returned.

Note the native substring() method can be particularly egregious because the start and end arguments may result in only half of some characters being returned, so to speak.

Version utilities

  • migrate()

A single migrate() function to handle the migration of JSON files with a required version entry. This function can be used in conjunction with the configuration utilities but does not have to be.

  • The migrate function takes json, migrationMap and latestVersion arguments. Perhaps the easiest way to demonstrate its use is by way of an extensive example.

Your application should maintain a list of version numbers. A new version number should be used every time the format of the requisite JSON file needs to be migrated:

const VERSION_1_5 = "1.5",
      VERSION_2_0 = "2.0",
      VERSION_5_0 = "5.0",
      VERSION_5_1 = "5.1";

module.exports = {
  VERSION_1_5,
  VERSION_2_0,
  VERSION_5_0,
  VERSION_5_1
};

These version numbers, together with their corresponding migration functions, should then be required or imported for use by the function that handles the migration:

const { migrateConfigurationToVersion_2_0 } = require("./configuration/version_2_0"),
      { migrateConfigurationToVersion_5_0 } = require("./configuration/version_5_0"),
      { migrateConfigurationToVersion_5_1 } = require("./configuration/version_5_1"),
      { VERSION_1_5, VERSION_2_0, VERSION_5_0, VERSION_5_1 } = require("./versions");

A map must then be created that is passed to the migrate() function along with the JSON and the latest version:

function migrateConfigurationFile() {
  let json = readRCFile();

  const migrationMap = {
          [ VERSION_1_5 ]: migrateConfigurationToVersion_2_0,
          [ VERSION_2_0 ]: migrateConfigurationToVersion_5_0,
          [ VERSION_5_0 ] :migrateConfigurationToVersion_5_1
        },
        latestVersion = VERSION_5_1;

  json = migrate(json, migrationMap, latestVersion);

  writeRCFile(json);
}

Note carefully the matching of the keys to their corresponding values. Each key matches the version that the migrate() function finds in the JSON. It therefore must apply the requisite migration function to migrate the JSON to the next version.

Lastly, the migration function must have the prescribed signature and return the migrated JSON. Again an example will suffice:

const { VERSION_2_0 } = require("../versions");

function migrateConfigurationToVersion_2_0(configuration) {
  const version = VERSION_2_0;

  Object.assign(configuration, {
    version
  });

  return configuration;
}

In this admittedly somewhat trivial example, all the migration function does is to update the version number. Exactly how the JSON otherwise changes is immaterial but the version number must be updated in this way otherwise the migrate() function will loop indefinitely.

Asynchronous utilities

  • whilst()
  • forEach()
  • sequence()
  • eventually()
  • repeatedly()

These functions generally take either an operation or an array of operations, an operation being a function that mutates a context rather than returning a value. They also take a done() function and an optional context argument. They all pass a next() function to the operations followed by the done() function, the context and then an index argument. Operations can call the done() function instead of the next() function in order to terminate early.

  • The whilst() function takes a single operation, which it calls each time the operation invokes the given next() function or until the operation invokes the given done() function. The operation can also force termination by returning a truthy value, in which case it must not call the given next() or done() functions. In the example below the operation will be executed ten times:
const context = {}; ///

const operation = (next, done, context, index) => {
  const terminate = (index === 9);

  if (terminate) {
    done();
  } else {
    ...

    next();
  }
}

whilst(operation, () => {
  /// done
}, context);
  • The forEach() function takes an array as the first argument followed by a single operation, which it calls for each element of the array unless the operation invokes the given done() function. If the done() function is never invoked by the operation, it is called once each of the array elements has been passed to the operation, provided the operationinvokes the given next () function each time. In the example below the operation will be executed four times:
const context = {};

const operation = (element, next, done, context, index) => {
  const terminate = (element === 3);

  if (terminate) {
    done();
  } else {
    ...

    next();
  }
}

const array = [0, 1, 2, 3, 4, 5];

forEach(array, operation, () => {
  /// done
}, context);
  • The sequence() function takes an array of operations, which it calls in turn unless the operation invokes the given done() function. If the done() function is never invoked by a operation, it is called once each of the operations have been called, provided each operation invokes the given next () function. In the example below each of the operations bar the last is executed:
const context = {};

const firstOperation = (next, done, context, index) => { next(); },
      secondOperation = (next, done, context, index) => { next(); },
      thirdOperation = (next, done, context, index) => { done(); },
      lastOperation = (next, done, context, index) => { next(); },
      operation = [
        firstOperation,
        secondOperation,
        thirdOperation,
        lastOperation
      ];

sequence(operations, () => {
  /// done
}, context);
  • The eventually() function takes an array of operations, each of which it calls immediately without waiting for the operations to invoke the given next() functions. When each of the operations has invoked the given next() function, it will call the done() function. Note that in this case invoking the done() function from within a operation will not halt the execution of other operations, it is passed as an argument only for the sake of convention. In the example below each of the operations is executed:
const context = {};

const firstOperation = (next, done, context, index) => { next(); },
      secondOperation = (next, done, context, index) => { next(); },
      thirdOperation = (next, done, context, index) => { done(); },
      operations = [
        firstOperation,
        secondOperation,
        thirdOperation
      ];

eventually(operations, () => {
  /// done
}, context);
  • The repeatedly() function takes a single operation and a length argument, immediately calling the operation a length number of times without waiting for it to invoke the given next() function each time. When the operation has invoked the given next() function a length number of times, it will call the done() function. Note that in this case invoking the done() function from within the operation will not halt its execution the requisite number of times, it is passed as an argument only for the sake of convention. In the example below the operation is executed ten times:
const context = {};

const operation = (next, done, context, index) => {
  ...

  next();
};

const length = 10;

repeatedly(operation, length, () => {
  // done
}, context);

Building

Automation is done with npm scripts, have a look at the package.json file. The pertinent commands are:

npm run build-debug
npm run watch-debug

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