In JavaScript, three dots ( … ) are used for both the Spread and Rest operators. Spread and Rest perform different actions. Let’s learn what the JavaScript Spread & Rest Operators do.

JavaScript Spread Operator

The JavaScript Spread Operator ( … ) allows us to copy and split an Array or Object into another Array or Object.

Let’s look at an example of the Spread Operator in use:

const numbers = [1, 2, 3];
const newNumbers = [4, 5, 6];
const joinNumbers [...numbers, ...newNumbers];

console.log(joinNumbers);
// Output: [1, 2, 3, 4, 5, 6]

JavaScript Rest Operator

In JavaScript, the Rest Operator is used in a very different way to the Spread Operator. The Rest Operator puts the rest of some specific values into an array.

What does this mean?

The Rest Operator allows a function to accept an indefinite number of arguments as an array.

Let’s look at an example of the Rest Operator in use:

function sumOfNumbers(...numbers) {
    let value = 0;
    for(const num of numbers) {
        total += num;
    }
    return total;
}

console.log( sumOfNumbers(1, 2, 3) );
// Output: 6

console.log( sumOfNumbers(5, 10, 15, 20) );
// Output: 50

Conclusion

The JavaScript Spread & Rest Operators can prove to be very useful for your web applications.

Learn about Destructuring in JavaScript.