Function that merges arrays into one in JavaScript

Let's now implement the merge function, which takes an arbitrary number of arrays as parameters and merges their elements into one array.

Here is an example of how our function works:

let result = merge([1, 2, 3], [4, 5, 6], [7, 8, 9]);
console.log(result); // shows [1, 2, 3, 4, 5, 6, 7, 8, 9]

Let's get down to implementation. Let's first get the passed arrays as a single two-dimensional one:

merge([1, 2, 3], [4, 5, 6], [7, 8, 9]);

function merge(...arrs){
	console.log(arrs); // shows  [ [1, 2, 3,] [4, 5, 6], [7, 8, 9] ]
}

Let's now merge this two-dimensional array into a one-dimensional one. We use the concat method and the spread operator for this:

let arrs   = [ [1, 2, 3,], [4, 5, 6], [7, 8, 9] ];

let result = [].concat(...arrs);
console.log(result); // shows [1, 2, 3, 4, 5, 6, 7, 8, 9]

Let's add this code to our merge function:

function merge(...arrs) {
	return [].concat(...arrs);
}

let result = merge([1, 2, 3], [4, 5, 6], [7, 8, 9]);
console.log(result); // shows [1, 2, 3, 4, 5, 6, 7, 8, 9]

As you can see, this function also turned out to be very concise.