promisemaker

promisemaker 0.1.3 - documentation

Converts methods using callbacks into methods returning promises. Can convert a whole module/library (like fs) at once.

Thomas Frank, Nodebite, April 2016

Install

Install: npm install promisemaker (or incude as an dependency in your package.json file)

Usage

Simple example - convert the fs module

var pm = require("promisemaker");
 
// Wrap the fs module with promisemaker
var fs = pm( require("fs") );
 
// Now all methods return promises
fs.readFile("./package.json","utf8").then(
  function(x){
    console.log("Resolved", x);
  },
  function(x){
    console.log("Rejected",x);
  }
);

Advanced example - convert the mysql module

var pm = require("promisemaker");
 
var mysql = require('mysql');
 
// When it comes to the mysql module
// what we want to wrap is an instance
// the "connection"
 
var connection = pm(
  mysql.createConnection({
    "host": "127.0.0.1",
    "user": "root",
    "password": "dbPassword",
    "database": "someDatabase"
  }),
  {
    // The connection object of the mysql module
    // has a method called query
    // that returns rows and fields to the original
    // callback function as different arguments
    // here we tell promisemaker
    // to map this to an object with properties
    mapArgsToProps: {query: ["rows", "fields"]}
  }
);
 
connection.query('SHOW TABLES').then(
  function(x){
    console.log("Resolved", x.rows);
  },
  function(x){
    console.log("Rejected",x);
  }
);

ES7 and await

Although we use traditional ES6 above, obviously one of the cool things with promisemaker is that if we run it in an ES7 environment we can use it with awaits:

var pm = require("promisemaker");
 
// Wrap the fs module with promisemaker
var fs = pm( require("fs") );
 
// Use with await in ES7
var fileContents = await fs.readFile("./package.json","utf8");

Settings

As you saw in the advanced example promisemaker has a number of settings you can send to it as a a second argument. Their usage and default values are as follows:

{
  // rejectOnErrors: If set to false resolves even on errors.
  rejectOnErrors: true,
  // syncFuncs : Strings and regexps to match function names against
  // when deciding if a function is synchronous.
  syncFuncs: [ /.*?Sync$/ ],
  // syncFuncsReturnPromises: If false returns the value directly
  // for a synchronous function, instead of a promise
  syncFuncsReturnPromises: true,
  // If the callback receives several arguments (apart from an error)
  // then we can map the arguments into property names.
  // If a mapping exists the promises receives an object,
  // otherwise it receives the argument array.
  mapArgsToProps: {/*"someFuncName": ["prop1", "prop2"]*/}
}