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11.5 JS Function Apply

Method Reuse

With the apply() method, you can write a method that can be used on different objects.

The JavaScript apply() Method

The apply() method is similar to the call() method (previous chapter).
In this example the fullName method of person is applied on person1:

Example 1: JS Functions - The JavaScript apply() Method

var person = {
  fullName: function() {
    return this.firstName + " " + this.lastName;
  }
}
var person1 = {
  firstName: "Mary",
  lastName: "Doe"
}
person.fullName.apply(person1);  // Will return "Mary Doe"

The Difference Between call() and apply()

The difference is:
The call() method takes arguments separately.
The apply() method takes arguments as an array.
The apply() method is very handy if you want to use an array instead of an argument list.

The apply() Method with Arguments

The apply() method accepts arguments in an array:

Example 2: JS Functions - The apply() Method with Arguments

var person = {
  fullName: function(city, country) {
    return this.firstName + " " + this.lastName + "," + city + "," + country;
  }
}
var person1 = {
  firstName:"John",
  lastName: "Doe"
}
person.fullName.apply(person1, ["Oslo", "Norway"]);

Compared with the call() method:

Example 3: JS Functions - The call() Method with Arguments

var person = {
  fullName: function(city, country) {
    return this.firstName + " " + this.lastName + "," + city + "," + country;
  }
}
var person1 = {
  firstName:"John",
  lastName: "Doe"
}
person.fullName.call(person1, "Oslo", "Norway");

Simulate a Max Method on Arrays

You can find the largest number (in a list of numbers) using the Math.max() method:

Example 4: JS Math.max() part 1

Math.max(1,2,3);  // Will return 3

Since JavaScript arrays do not have a max() method, you can apply the Math.max() method instead.

Example 5: JS Math.max() part 2

Math.max.apply(null, [1,2,3]); // Will also return 3

The first argument (null) does not matter. It is not used in this example.
These examples will give the same result:

Example 6: JS Math.max() part 3

Math.max.apply(Math, [1,2,3]); // Will also return 3

Example 7: JS Math.max() part 4

Math.max.apply(" ", [1,2,3]); // Will also return 3

Example 8: JS Math.max() part 5

Math.max.apply(0, [1,2,3]); // Will also return 3

JavaScript Strict Mode

In JavaScript strict mode, if the first argument of the apply() method is not an object, it becomes the owner (object) of the invoked function. In "non-strict" mode, it becomes the global object.

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Module 11. JS Functions

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Example files created in this module:
JS Functions - Function Declaration JS Functions - Function Expressions part 1 JS Functions - Function Expressions part 2 JS Functions - The Function() Constructor part 1 JS Functions - The Function() Constructor part 2 JS Functions - Self-Invoking Functions JS Functions - Functions Can Be Used as Values part 1 JS Functions - Functions Can Be Used as Values part 2 JS Functions are Objects part 1 JS Functions are Objects part 2 JS Arrow Functions part 1 JS Arrow Functions part 2 JS Default Parameters JS Functions - Default Parameter Values JS functions - The Rest Parameter JS Functions - Finding the largest number JS Functions - Sum of all arguments JS Functions - Invoking a Function as a Function part 1 JS Functions - Invoking a Function as a Function part 2 JS Functions - The Global Object JS Functions - Invoking a Function as a Method part 1 JS Functions - Invoking a Function as a Method part 2 JS Functions - Invoking a Function with a Function Constructor JS Functions - All Functions are Methods JS Functions - The JavaScript call() Method part 1 JS Functions - The JavaScript call() Method part 2 JS Functions - The JavaScript call() Method with Arguments JS Functions - The JavaScript apply() Method JS Functions - The apply() Method with Arguments JS Functions - The call() Method with Arguments JS Math.max() part 1 JS Math.max() part 2 JS Math.max() part 3 JS Math.max() part 4 JS Math.max() part 5 JS Function bind() part 1 JS Function bind() part 2 JS Function bind() part 3 JS Function bind() part 4 JS Functions - Global Variables part 1 JS Functions - Global Variables part 2 JS Functions - Global Variables part 3 JS Function Closures - Counter Dilemma part 1 JS Function Closures - Counter Dilemma part 2 JS Function Closures - Counter Dilemma part 3 JS Function Closures - Nested Functions JS Closures