Swapping variables is a common task in programming, and there are several ways to do it without using a third variable. In this post, we'll explore five different methods in JavaScript, each with a detailed explanation.

1. Addition and Subtraction

This method involves simple arithmetic operations:

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

console.log('After Addition and Subtraction:');
console.log('a:', a); // 40
console.log('b:', b); // 20

Explanation:

a = a + b; combines the values of a and b and stores the result in a.
b = a - b; subtracts the new value of b (which is a) from a to get the original value of a.
a = a - b; subtracts the new value of b (original a) from a to get the original value of b.

2. Multiplication and Division

Another arithmetic method, but using multiplication and division. Note that this method assumes a and b are non-zero to avoid division by zero:

a = 20;
b = 40;

a = a * b;
b = a / b;
a = a / b;

console.log('After Multiplication and Division:');
console.log('a:', a); // 40
console.log('b:', b); // 20

Explanation:

a = a * b; multiplies the values of a and b and stores the result in a.
b = a / b; divides the new value of a by b to get the original value of a.
a = a / b; divides the new value of a by the new value of b to get the original value of b.

3. Using Bitwise XOR

Bitwise operations can also be used to swap variables:

a = 20; 
b = 40;

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

console.log('After Bitwise XOR:');
console.log('a:', a); // 40
console.log('b:', b); // 20

Explanation:

a = a ^ b; stores the result of the bitwise XOR of a and b in a.
b = a ^ b; stores the result of the bitwise XOR of the new a and b (which is the original a) in b.
a = a ^ b; stores the result of the bitwise XOR of the new a and b (which is the original b) in a.

4. Using Array Destructuring

A more modern and elegant approach in JavaScript uses array destructuring:

a = 20;
b = 40;

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

console.log('After Array Destructuring:');
console.log('a:', a); // 40
console.log('b:', b); // 20

Explanation:

[a, b] = [b, a]; swaps the values of a and b using array destructuring assignment. This is a concise and readable way to swap variables in modern JavaScript.

5. Compound Assignment Swap (Single Line Swap)

This clever method uses a combination of arithmetic and assignment in a single line:

a = 20;
b = 40;

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

console.log('After Compound Assignment Swap:');
console.log('a:', a); // 40
console.log('b:', b); // 20

Explanation:

a = a + b - (b = a); may look complex but it follows a specific sequence of operations due to how JavaScript evaluates expressions. Here's what happens:

1. (b = a) assigns the value of a to b.
2. Then, a + b - (b = a) becomes a + a - a, which effectively swaps the values of a and b.

In summary, each of these methods achieves the same result of swapping variables a and b without using a third variable, showcasing different techniques in JavaScript.