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function.call

The call() method calls a function with a given this value and arguments provided individually.

Note: While the syntax of this function is almost identical to that of apply(), the fundamental difference is that call() accepts an argument list, while apply() accepts a single array of arguments.

Syntax

function.call(thisArg, arg1, arg2, ...)

Parameters

thisArg
Optional. The value of this provided for the call to a function. Note that this may not be the actual value seen by the method: if the method is a function in non-strict mode , null and undefined will be replaced with the global object and primitive values will be converted to objects.
arg1, arg2, ...
Optional. Arguments for the function.

Return value

The result of calling the function with the specified this value and arguments.

Description

A different this object can be assigned when calling an existing function. this refers to the current object, the calling object. With call, you can write a method once and then inherit it in another object, without having to rewrite the method for the new object.

Examples

Using call to chain constructors for an object

You can use call to chain constructors for an object, similar to Java. In the following example, the constructor for the Product object is defined with two parameters, name and price. Two other functions Food and Toy invoke Product passing this and name and price. Product initializes the properties name and price, both specialized functions define the category.

function Product(name, price) {
  this.name = name;
  this.price = price;
}

function Food(name, price) {
  Product.call(this, name, price);
  this.category = 'food';
}

function Toy(name, price) {
  Product.call(this, name, price);
  this.category = 'toy';
}

var cheese = new Food('feta', 5);
var fun = new Toy('robot', 40);

Using call to invoke an anonymous function

In this purely constructed example, we create an anonymous function and use call to invoke it on every object in an array. The main purpose of the anonymous function here is to add a print function to every object, which is able to print the right index of the object in the array. Passing the object as this value was not strictly necessary, but is done for explanatory purpose.

var animals = [
  { species: 'Lion', name: 'King' },
  { species: 'Whale', name: 'Fail' }
];

for (var i = 0; i < animals.length; i++) {
  (function(i) {
    this.print = function() {
      console.log('#' + i + ' ' + this.species
                  + ': ' + this.name);
    }
    this.print();
  }).call(animals[i], i);
}

Using call to invoke a function and specifying the context for 'this'

In the example below, when we call greet the value of this will be bound to object obj.

function greet() {
  var reply = [this.person, 'Is An Awesome', this.role].join(' ');
  console.log(reply);
}

var obj = {
  person: 'Douglas Crockford', role: 'Javascript Developer'
};

greet.call(obj);  // Douglas Crockford Is An Awesome Javascript Developer

Using call to invoke a function and without specifying the first argument

In the example below, we invoke the display function without passing the first argument. If the first argument is not passed, the value of this is bound to the global object.

var sData = 'Wisen';
            
function display(){
  console.log('sData value is %s ', this.sData);
}

display.call();  // sData value is Wisen 

Specifications

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari
Basic support Yes Yes Yes Yes Yes Yes
Feature Android webview Chrome for Android Edge mobile Firefox for Android Opera Android iOS Safari Samsung Internet
Basic support Yes Yes Yes Yes Yes Yes ?

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call