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1.1.33 • Public • Published

A function is a set of statements that performs a task or calculates a value.
📦 Node.js, 🌐 Web, 📜 Files, 📰 JSDoc, 📘 Wiki.

Functions are one of the fundamental building blocks in JavaScript. It is similar to a procedure—a set of statements that performs a task or calculates a value (1). It can accept some parameters, and may define some local variables necessary for performing the desired operation. These parameters and local variables are contained in the scope of the function, and cannot be accessed from the outside. However, a function can access variables external to itself (as long as they are not overridden), such as global variables or variables in the scope this function is encapsulated in. A nested function can access free variables that are defined in outer scopes, even when it is being invoked away from where it is defined. It does this by capturing the free variables (by reference) into a closure (1). Closure, arrow functions, and more, are functional language features based on lambda calculus.

This package includes a number of methods to transform functions. This enables you to obtain a desired function by transforming the behavior of existing functions (without actually executing them). The result of a function can be manipulated with negate. In case a pure function is expensive, its results can cached with memoize. Parameters of a function can be manipulated with reverse, spread, unspread. reverse flips the order of parameters, spread spreads the first array parameter of a function, and unspread combines all parameters into the first parameter (array). If you want some functional behavior, compose, composeRight, curry, and curryRight can be used. composeRight is also known as pipe-forward operator or function chaining. If you are unfamiliar, Haskell is a great purely functional language, and there is great haskell beginner guide to learn from.

To control invocation time of a function, use delay. A function can be rate controlled with restrict, debounce, debounceEarly, throttle, throttleEarly. debounce and debounceEarly prevent the invocation of a function during hot periods (when there are too many calls), and can be used for example to issue AJAX request after user input has stopped (for certain delay time). throttle and throttleEarly can be used to limit the rate of invocation of a function, and can be used for example to minimize system usage when a user is constantly refreshing a webpage. Except restrict, all rate/time control methods can be flushed (flush()) to invoke the target function immediately, or cleared (clear()) to disable invocation of the target function.

In addition, is, isAsync, isGenerator, name, and length obtain metadata (about) information on a function. To attach a this to a function, use bind. A few generic functions are also included: NOOP, FALSE, TRUE, IDENTITY, COMPARE, ARGUMENTS.

This package is available in Node.js and Web formats. To use it on the web, simply use the extra_function global variable after loading with a <script> tag from the jsDelivr CDN.

Stability: Experimental.

const xfunction = require('extra-function');
// import * as xfunction from "extra-function";
// import * as xfunction from "https://unpkg.com/extra-function/index.mjs"; (deno)

var a = xfunction.composeRight(x => x*x, x => x+2);
// → 102

var a = xfunction.curry((x, y) => x+y);
// → 7

var a = xfunction.unspread(Math.max);
a([2, 3, 1]);
// → 1.25


Property Description
NOOP Do nothing.
FALSE Return false.
TRUE Return false.
IDENTITY Return the same (first) value.
COMPARE Compare two values.
ARGUMENTS Return the arguments passed as a array.
name Get the name of a function.
length Get the number of parameters of a function.
bind Bind this-object, and optional prefix arguments to a function.
call Invoke a function with specified this-object, and arguments provided individually.
apply Invoke a function with specified this-object, and arguments provided as an array.
is Check if value is a function.
isAsync Check if value is an async function.
isGenerator Check if value is a generator function.
contextify Contextify a function by accepting the first parameter as this-object.
decontextify Decontextify a function by accepting this-object as the first argument.
negate Generate a result-negated version of a function.
memoize Generate result-cached version of a function.
reverse Generate a parameter-reversed version of a function.
spread Generate a (first) parameter-spreaded version of a function.
unspread Generate a (first) parameter-collapsed version of a function.
attach Attach prefix arguments to leftmost parameters of a function.
attachRight Attach suffix arguments to rightmost parameters of a function.
compose Compose functions together, in applicative order.
composeRight Compose functions together, such that result is piped forward.
curry Generate curried version of a function.
curryRight Generate right-curried version of a function.
defer Generate deferred version of a function, that executes after the current stack has cleared.
delay Generate delayed version of a function.
restrict Generate restricted-use version of a function.
restrictOnce Restrict a function to be used only once.
restrictBefore Restrict a function to be used only upto a certain number of calls.
restrictAfter Restrict a function to be used only after a certain number of calls.
debounce Generate debounced version of a function.
debounceEarly Generate leading-edge debounced version of a function.
throttle Generate throttled version of a function.
throttleEarly Generate leading-edge throttled version of a function.


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  • wolfram77