How to swap two variables in JavaScript

Question

I have this two variables:

var a = 1,
    b = 2;

My question is how to swap them? Only this variables, not any objects.

Answer 1

Here's a one-liner to swap the values of two variables.
Given variables a and b:

b = [a, a = b][0];

Demonstration below:

var a=1,
    b=2,
    output=document.getElementById('output');

output.innerHTML="<p>Original: "+a+", "+b+"</p>";

b = [a, a = b][0];

output.innerHTML+="<p>Swapped: "+a+", "+b+"</p>";

<div id="output"></div>

Answer 2

ES6 (Firefox and Chrome already support it (Destructuring Assignment Array Matching)):

let a = 5, b = 6;
[a, b] = [b, a];
console.log(`${a} ${b}`);

Answer 3

You can do this:

var a = 1,
    b = 2,
    tmp;
tmp = a;
a = b;
b = tmp;

For readability and maintainability, this can't be beat (at least in JavaScript). Anybody maintaining the code (including you six months from now) will know exactly what's going on.

Since these are integers, you can also use any number of clever tricks¹ to swap without using a third variable. For instance you can use the bitwise xor operator:

let a = 1, b = 2;
a = a ^ b;
b = a ^ b;
a = a ^ b;
    
console.log('a is now:', a);
console.log('b is now:', b);

This is called the XOR swap algorithm. Its theory of operation is described in this Wikipedia article.

¹"The competent programmer is fully aware of the limited size of his own skull. He therefore approaches his task with full humility, and avoids clever tricks like the plague." — Edsger W. Dijkstra

Answer 4

Don't use the code below. It is not the recommended way to swap the values of two variables (simply use a temporary variable for that). It just shows a JavaScript trick.

This solution uses no temporary variables, no arrays, only one addition, and it's fast. In fact, it is sometimes faster than a temporary variable on several platforms.
It works for all numbers, never overflows, and handles edge-cases such as Infinity and NaN.

a = b + (b=a, 0)

It works in two steps:

• (b=a, 0) sets b to the old value of a and yields 0
• a = b + 0 sets a to the old value of b

Answer 5

Since ES6, you can also swap variables more elegantly:

var a = 1,
    b = 2;

[a, b] = [b, a];

console.log('a:', a, 'b:', b); // a: 2 b: 1

Answer 6

Here's a one-liner, assuming a and b exist already and have values needing to be swapped:

var c=a, a=b, b=c;

As @Kay mentioned, this actually performs better than the array way (almost 2x as fast).

Answer 7

You can now finally do:

let a = 5;
let b = 10;

[a, b] = [b, a]; // ES6

console.log(a, b);

Answer 8

You could use a temporary swap variable or XOR.

a = a ^ b
b = a ^ b
a = a ^ b

This is just a basic logical concept and works in every language that supports XOR operation.

edit: see the Comments. Forgot to tell that this works for sure only with integer. Assumed the integer variables from question's thread

Answer 9

Use a third variable like this:

var a = 1,
    b = 2,
    c = a;

a = b; // must be first or a and b end up being both 1
b = c;

---

DEMO - Using a third variable

---

Answer 10

As your question was precious "Only this variables, not any objects. ", the answer will be also precious:

var a = 1, b = 2

a=a+b;
b=a-b;
a=a-b;

it's a trick

And as Rodrigo Assis said, it "can be shorter "

 b=a+(a=b)-b;

Demo: http://jsfiddle.net/abdennour/2jJQ2/

Answer 11

ES6 Destructuring:

Using an array: [a, b] = [b, a]; // my favorite

Using an object: {a, b} = {a:b, b:a}; // not bad neither

Answer 12

How could we miss these classic oneliners

var a = 1, b = 2
a = ({a:b, _:(b=a)}).a;

And

var a = 1, b = 2
a = (_=b,b=a,_);

The last one exposes global variable '_' but that should not matter as typical javascript convention is to use it as 'dont care' variable.

Answer 13

I see kind of programming olympiad here. One more tricky one-line solution:

b = (function(){ a=b; return arguments[0]; })(a);

Fiddle: http://jsfiddle.net/cherniv/4q226/

Answer 14

Single line swapping

a = a^b^(b^=(a^b));

Answer 15

var a = 5;
var b = 10;

b = [a, a = b][0];
//or
b = [a, a = b];
b = b[0];

//or
b = [a, b];
a = b[1];
b = b[0];


alert("a=" + a + ',' + "b=" + b);

remove or comment the 2 //or's and run with the one set of code

http://jsfiddle.net/USdv8/57/

Answer 16

We are able to swap var like this :

var val1 =  117,
    val2 = 327;

val2 = val1-val2; 
console.log(val2);
val1 = val1-val2;
console.log(val1);
val2 = val1+val2;
console.log(val2);

Answer 17

Till ES5, to swap two numbers, you have to create a temp variable and then swap it. But in ES6, its very easy to swap two numbers using array destructuring. See example.

let x,y;
[x,y]=[2,3];
console.log(x,y);      // return 2,3

[x,y]=[y,x];
console.log(x,y);      // return 3,2

Know more about JavaScript ES6 destructuring

Answer 18

let a = 2, b = 4;
[b, a] = [a, b];

a more verbose approach would be

let a = 2, b = 4;
a = [a, b];
b = a[0];
a = a[1];

Answer 19

Because I hear this method runs slower:

b = [a, a = b][0];

If you plan on storing your vars in an object (or array), this function should work:

function swapVars(obj, var1, var2){
    let temp = obj[var1];
    obj[var1] = obj[var2];
    obj[var2] = temp;
}

Usage:

let test = {a: 'test 1', b: 'test 2'};

console.log(test); //output: {a: 'test 1', b: 'test 2'}

swapVars(test, 'a', 'b');

console.log(test); //output: {a: 'test 2', b: 'test 1'}

Answer 20

We can use the IIFE to swap two value without extra parameter

var a = 5, b =8;
b = (function(a){ 
    return a 
}(a, a=b));

document.write("a: " + a+ "  b:  "+ b);