JavaScript Rest Parameters

How I Finally Understood JavaScript Rest Parameters (...args)

As a beginner learning JavaScript, I was confused when I first saw the ...args syntax. I thought it was something very advanced. After practising, I realised it is actually simple and very useful.

What is a Rest Parameter?

A rest parameter allows us to collect multiple arguments into a single array.

Example:

function showNumbers(...numbers) {
    console.log(numbers);
}

showNumbers(10, 20, 30, 40);

Output:

[10, 20, 30, 40]

The ...numbers syntax collects all values and stores them in an array called numbers.

Why Use Rest Parameters?

Sometimes we don't know how many values a user will pass to a function.

For example:

sum(10, 20);
sum(10, 20, 30);
sum(10, 20, 30, 40, 50);

Instead of creating many parameters, we can use a rest parameter.

Example: Sum All Numbers

function sum(...numbers) {
    let total = 0;

    for (let num of numbers) {
        total += num;
    }

    return total;
}

console.log(sum(10, 20, 30, 40));

Output:

100

What I Learned

• ...args collects multiple values.
• Rest parameters create an array.
• They are useful when we don't know the number of arguments.
• They are commonly used in modern JavaScript.

As a beginner, practising small examples helped me understand this concept much better than just reading the theory.