A few neat things you can do with the vanilla JS spread syntax operator

The spread syntax operator (...) takes an array or object (or other iterable) and expands its items into their own individual values.

let sandwiches = ['tuna', 'turkey', 'pb&j'];

// logs ["tuna", "turkey", "pb&j"]
console.log(sandwiches);

// logs tuna turkey pb&j
console.log(...sandwiches);

The spread operator can only be used inside of functions, arrays and objects. You cannot use it on its own.

This, for example, would throw an error.

// Uncaught SyntaxError: Unexpected token '...'
...sandwiches;

The spread operator can be really useful for some specific situations.

Passing an array of arguments into a function as individual arguments

Imagine you have a function, add(), that accepts two numbers as arguments and adds them together.

// Add two numbers together
function add (num1, num2) {
	return num1 + num2;
}

And, you have an array of numbers.

let numbers = [4, 2];

Instead of using bracket notation to get each number and pass it in individually, you can use the spread operator to break the numbers array into individual items.

// Instead of this...
// returns 6
add(numbers[0], numbers[1]);

// You can do this...
// returns 6
add(...numbers);

Combine or copy an array or object

You can use the spread operator to combine or copy arrays or objects.

/**
 * Arrays
 */

// Some arrays
let sandwiches1 = ['tuna', 'turkey', 'pb&j'];
let sandwiches2 = ['chicken', 'pb&j'];

// Copy an array
// Works like Array.from(sandwiches)
let sandwichesCopy = [...sandwiches1];

// Combine two arrays
// Works like sandwiches1.concat(sandwiches2)
let moreSandwiches = [...sandwiches1, ...sandwiches2];


/**
 * Objects
 */

// Some objects
let radagast1 = {
	color: 'brown',
	druid: true
};
let radagast2 = {
	skills: 'Talks with animals',
	druid: false
};

// Copy an object
// Works like Object.assign({}, radagst1);
let radagastCopy = {...radagast1};

// Combine two objects
// Works like Object.assign({}, radagast1, radagast2);
let moreRadagast = {...radagast1, ...radagast2};

For situations like this, the spread operator can provide a simpler syntax that makes the intent of your code more clear and obvious.

These approaches aren’t inherently better than using methods like Array.from() or Object.assign(), so ultimately, use whichever approach you find most comfortable and easy to work with.