JavaScript Program to Swap Two Numbers Easily

You can swap two numbers in JavaScript using a temporary variable like let temp = a; a = b; b = temp; or using array destructuring like [a, b] = [b, a];.

Examples

Inputa = 5, b = 10

Outputa = 10, b = 5

Inputa = -3, b = 7

Outputa = 7, b = -3

Inputa = 0, b = 0

Outputa = 0, b = 0

How to Think About It

To swap two numbers, think of holding one number temporarily so you don't lose it when you overwrite its variable. You store the first number in a temporary place, assign the second number to the first variable, then put the stored number into the second variable. Alternatively, JavaScript lets you swap directly using array destructuring without a temporary variable.

Algorithm

1

Get the two numbers to swap, call them a and b.

2

Store the value of a in a temporary variable temp.

3

Assign the value of b to a.

4

Assign the value of temp to b.

5

Return or print the swapped values.

Code

javascript

let a = 5;
let b = 10;

// Using a temporary variable
let temp = a;
a = b;
b = temp;

console.log('After swapping: a =', a, ', b =', b);

Output

After swapping: a = 10 , b = 5

Dry Run

Let's trace swapping a=5 and b=10 through the code

1

Initial values

a = 5, b = 10

2

Store a in temp

temp = 5

3

Assign b to a

a = 10

4

Assign temp to b

b = 5

5

Final swapped values

a = 10, b = 5

Step	a	b	temp
Initial	5	10	undefined
Store a	5	10	5
Assign b to a	10	10	5
Assign temp to b	10	5	5

Why This Works

Step 1: Temporary storage

We use a temporary variable temp to hold the value of a so it is not lost when we overwrite a.

Step 2: Overwrite first variable

We assign the value of b to a, so now a holds the second number.

Step 3: Restore second variable

We assign the stored value in temp back to b, completing the swap.

Alternative Approaches

Array destructuring

javascript

let a = 5;
let b = 10;

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

console.log('After swapping: a =', a, ', b =', b);

This method is shorter and more modern but requires understanding of array destructuring.

Arithmetic operations

javascript

let a = 5;
let b = 10;

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

console.log('After swapping: a =', a, ', b =', b);

This method swaps without extra memory but can cause overflow with very large numbers.

Complexity: O(1) time, O(1) space

Time Complexity

Swapping two numbers involves a fixed number of steps, so it runs in constant time O(1).

Space Complexity

Only a few variables are used, so space complexity is constant O(1).

Which Approach is Fastest?

All methods run in O(1) time; array destructuring is concise and readable, arithmetic avoids extra variables but risks overflow.

Approach	Time	Space	Best For
Temporary variable	O(1)	O(1)	Simple and clear for beginners
Array destructuring	O(1)	O(1)	Modern, concise syntax
Arithmetic operations	O(1)	O(1)	No extra variables, but risky with large numbers