Functions in JavaScript provide organized, reusable code to perform a set of actions. Functions simplify the coding process, prevent redundant logic, and make code easier to follow. This topic describes the declaration and utilization of functions, arguments, parameters, return statements and scope in JavaScript.

Syntax

• function example(x) { return x }

• var example = function (x) { return x }

• (function() { … })(); // Immediately Invoked Function Expression (IIFE)

• var instance = new Example(x);

• Methods

  • fn.apply(valueForThis[, arrayOfArgs])
  • fn.bind(valueForThis[, arg1[, arg2, …]])
  • fn.call(valueForThis[, arg1[, arg2, …]])

• ES2015+ (ES6+):

  • const example = x => { return x }; // Arrow function explicit return
  • const example = x => x; // Arrow function implicit return
  • const example = (x, y, z) => { … } // Arrow function multiple arguments
  • (() => { … })(); // IIFE using an arrow function

Remarks

For information on arrow functions, please view the Arrow Functions documentation.

Introduction

Function Scoping

Currying

Immediately Invoked Function Expressions (IIFE)

Binding this and arguments

Named Functions

Variadic function (with arbitrary number of arguments)

Anonymous Function

Default parameters

Function Composition

Partial Application

Passing arguments by reference or value

Call and apply

Function Arguments arguments object rest and spread parameters

Using the Return Statement

Get the name of a function object

Recursive Function

Functions as a variable

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