Function apply()

Why function.apply ?

The JavaScript apply () function is used to recall a function. Apply () contains the value and parameters in the assigned function.

Syntax:

function.apply(thisArg, [array])  

thisArg(optional): The this value is given for the call to a function.

array(optional): It is an array-like object.

---

Let’s understand the logic with a small example.

        function sum(a,b) {
            return a + b;
        }
        
        let res = sum.apply(null,[2,5])
        console.log(res)

7

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The apply () method is very similar to the call () method. The apply () method takes an array as a variable. The Call () method takes individual arguments.

        let users = {
            user1: function (name, surname) {
                return "age: " + this.age + "  " + "country: " + this.country;
            }
        }
        let use1 = {
            age: 32,
            country: "England"
        }

        let arr = users.user1.apply(use1, ["rick", "allen"])
        console.log(arr)

age: 32 country: England

call;

        let users = {
            user1: function ( name, surname ) {
                return "age: " + this.age + "  " + "country: " + this.country;
            }
        }
        let use1 = {
            age: 32,
            country: "England"
        }

        let arr = users.user1.call( use1, "rick", "allen")
        console.log(arr)

age: 32 country: England

---

Function apply() Examples

Example 1

        function sum() {
            console.log(this);
            let sum = 0;
            for (var i = 0; i < arguments.length; i++) {
                sum += arguments[i];
            }
            return sum;
        }

        let result = sum.apply({
            name: "barry",
            surname: "quenn"
        }, [ 10 , 20 , 30 , 40]);
        console.log(result);

output:

name: “barry”, surname: “quenn”
100

---

Example 2

        let users = {
            nameAndSurname: function () {
                return this.name + " -" + this.surname;
            }
        }

        let user1 = { name: "oliver", surname: "clark" };
        let user2 = { name: "bob", surname: "adams" };
        let user3 = { name: "alex", surname: "black" };

        console.log( users.nameAndSurname.apply( user1 ) );
        console.log( users.nameAndSurname.apply( user2 ) );
        console.log( users.nameAndSurname.apply( user3 ) );

output:

oliver — clark
bob — adams
alex — black

---

Example 3

        let numbers = [ 1 , 2 , 3 , 4 , 5 , 6 ];
        let max = Math.max.apply(null, numbers);
        console.log(max);

output:

6

---

Example 4

        let numbers = [1, 2, 3, 4, 5, 6];
        let min = Math.min.apply(null, numbers);
        console.log(min);

output:

1

---

Example 5

        let txt = ["a", "b", "c", "d", "e"];
        let numbers = [1, 2, 3, 4, 5, 6];
        txt.push.apply(txt, numbers);
        console.log(txt);

output:

[“a”, “b”, “c”, “d”, “e”, 1, 2, 3, 4, 5, 6]

---

Example 6

        function nameAndUsername(name, job) {
            return "my name is " + name + "and I am a " + job
        }

        console.log(nameAndUsername.apply(null, ["rick", "teacher"]));
        console.log(nameAndUsername.apply(null, ["bob", "mathematician"]));
        console.log(nameAndUsername.apply(null, ["alex", "physic"]));

output:

my name is rickand I am a teacher
my name is boband I am a mathematician
my name is alexand I am a physic

---

Example 7

        let friend = {
            car: true,
            lendCar: function (a) {
                this.car = a;
            }
        }

        let me = {
            car: true,
            gotCar: function () {
                return this.car === true;
            }
        };

        friend.lendCar.apply(me, [true]);
        console.log(me.gotCar());

output:

true

---

Example 8

apply

        let num1 = Number(prompt("number1: "));
        let num2 = Number(prompt("number2: "));

        function sum(a, b) {
            return this.a + this.b;
        };

        let num = {
            a: num1,
            b: num2,
        }

        let res = sum.apply(num);

        console.log(res)

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Browser Support

Chrome	yes
Edge	yes
Firefox	1
Internet Explorer	yes
Opera	yes
Safari	yes
Android webview	yes
Chrome for Android	yes
Edge mobile	yes
Firefox for Android	4
Opera Android	yes