How to swap two variables in JavaScript
JavascriptVariablesSwapJavascript Problem Overview
I have this two variables:
var a = 1,
b = 2;
My question is how to swap them? Only this variables, not any objects.
Javascript Solutions
Solution 1 - Javascript
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>
Solution 2 - Javascript
ES6 (Firefox and Chrome already support it (Destructuring Assignment Array Matching)):
let a = 5, b = 6;
[a, b] = [b, a];
console.log(`${a} ${b}`);
Solution 3 - Javascript
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
Solution 4 - Javascript
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)
setsb
to the old value ofa
and yields0
a = b + 0
setsa
to the old value ofb
Solution 5 - Javascript
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
Solution 6 - Javascript
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).
Solution 7 - Javascript
You can now finally do:
let a = 5;
let b = 10;
[a, b] = [b, a]; // ES6
console.log(a, b);
Solution 8 - Javascript
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
Solution 9 - Javascript
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
Solution 10 - Javascript
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;
Solution 11 - Javascript
ES6 Destructuring:
Using an array: [a, b] = [b, a]; // my favorite
Using an object: {a, b} = {a:b, b:a}; // not bad neither
Solution 12 - Javascript
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.
Solution 13 - Javascript
I see kind of programming olympiad here. One more tricky one-line solution:
b = (function(){ a=b; return arguments[0]; })(a);
Solution 14 - Javascript
Single line swapping
a = a^b^(b^=(a^b));
Solution 15 - Javascript
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
Solution 16 - Javascript
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);
Solution 17 - Javascript
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
Solution 18 - Javascript
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'}
Solution 19 - Javascript
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);
Solution 20 - Javascript
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];
Solution 21 - Javascript
Although the same answer is given previously, but here is a png to describe it.
Simplest form possible:
Solution 22 - Javascript
first way,
var a = 5, b = 9;
a = a - b;
b = a + b;
a = b - a;
console.log(a, b);
second way
var a = 19, b = 22;
[a, b] = [b, a];
console.log(a, b);
simple and clear answer.