JavaScript 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:

const person = {

  fullName: function() {

    return this.firstName + " " + this.lastName;

  }

}

const person1 = {

  firstName: "Mary",

  lastName: "Doe"

}

// This will return "Mary Doe":

person.fullName.apply(person1);


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:

<script>

const person = {

  fullName: function(city, country) {

    return this.firstName + " " + this.lastName + "," + city + "," + country;

  }

}

const person1 = {

  firstName:"John",

  lastName: "Doe"

}

document.getElementById("demo").innerHTML = person.fullName.apply(person1, ["Oslo", "Norway"]); 

</script>

Compared with the call() method:

EXAMPLE ❯


Simulate a Max Method on Arrays

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

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.

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

The first argument (null) does not matter. It is not used in this example.

These examples will give the same result:

EXAMPLE ❯


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.