5 ways to merge arrays in JavaScript (easy)
Tags: webdev, javascript, beginners, tutorial
Published: 2023-02-21 05:50:23


If you’re coding in JavaScript, chances are you’ve come across the need to merge two or more arrays. 

And while there's no one-size-fits-all approach to combining arrays, there are a few different ways you can go about it.

In this article, we'll be talking about five easy ways to use JavaScript to merge multiple arrays into one. 

We'll break down each method with examples and codes for each, so by the time you're finished reading, you'll have a clear understanding of which methods work best for your project. 

Let's dive in!

## What Is Array Merging?

So, you're thinking of merging arrays in JavaScript? Great! You have a few options for how to do this, which we'll cover later on. But first, let's dive into exactly what array merging means.

Array merging is the process of combining separate arrays into one single array. 

It's an incredibly useful task when coding because it allows you to join data from two or more different sources, giving your program more flexibility and power.

For example, you could use array merging to combine a list of employee names with a list of their respective departments. 

In the end, you'd have one unified array that contains all the relevant information about that particular team.

## Merging arrays using the Spread Operator

The Spread Operator is one of the easiest ways to merge two arrays in JavaScript. 

It takes elements from the second array and adds them to the first, creating a new merged object. 

To do this, you just need to use this syntax:

```
const newArray = [...arrayOne, ...arrayTwo];
```

This method works best if your arrays have only simple values like strings or numbers - it won't work with objects or nested arrays. But it's a great tool for quickly concatenating two arrays without having to loop through each element. 

Plus, you can use as many arrays as you like - just add as many spread operators as you need!

## Merging arrays using the `concat()` method

When it comes to merging arrays in JavaScript, one of the most popular and versatile methods is to use the `concat()` method. 

All you need to do is pass in two array parameters, and they'll be merged together into a single array. 

You can also pass in more than two arrays, and they will all be merged together.

Here's what the syntax looks like:

```javascript

var array1 = [1,2,3];

var array2 = [4,5,6];

var mergedArray = array1.concat(array2);

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

Keep in mind that you can also combine nested arrays with the `concat()` method. This is especially useful if you're dealing with two-dimensional arrays or more complex objects with multiple properties. 

Here's an example of how to combine a nested array:

```javascript
var array1 = [[4], [6], [11]];
var array2 = [[3], [7], [18]];
var mergedArray = array1.concat(array2);

console.log(mergedArray); // Output: [[4], [6], [11], [3], [7], [18]]
```

## Merging arrays using the `forEach()` method

Apart from the popular methods discussed above, you can also use the `forEach()` method to merge arrays. 

What is the `forEach()` method? Put simply, it's a special type of loop that cycles through the array and calls a callback function on each item in the array.

```js
const arr1 = [1, 2, 3];
const arr2 = [4, 5, 6];

const mergedArr = [];

arr1.forEach(item => {
  mergedArr.push(item);
});

arr2.forEach(item => {
  mergedArr.push(item);
});

console.log(mergedArr); // [1, 2, 3, 4, 5, 6]
```


We create two arrays `arr1` and `arr2`, and then we create an empty array `mergedArr` to hold the merged elements. 

We then use two separate `forEach()` loops to push the elements from `arr1` and `arr2` into `mergedArr`.

Finally, we log the `mergedArr` array to the console, which contains all the elements from both arrays.

## Merging arrays using `reduce()` method

The fifth and final way to merge arrays in JavaScript is by using the reduce() method. 

It’s quite powerful but also a bit complex, so if you want to learn more about it check out this guide.

The reduce() method takes in two parameters: a callback, and an initial value. 

The initial value is optional and it is what the accumulator will begin with when the method is called on an array.

The accumulator loops through each of the elements in the array and runs your callback function on each element, then stores the result until the loop is complete, giving you a single output (the merged array).

For example, let’s say we have two arrays that we want to merge:

```javascript
let arr1 = [1, 2, 3];
let arr2 = [4, 5];
```

To merge these two arrays using reduce(), we can do this:

```javascript
let mergedArray = [...arr1,...arr2].reduce(function(a,b) {return a.concat(b);}, []);

//output: [1, 2, 3, 4, 5]

```

As you can see here our initial value is `[]`, which means our accumulator will be empty when the loop begins and then add elements as it goes through each one.

## Conclusion

So there you have it - five easy ways to merge arrays in JavaScript. Now you have the tools to quickly and easily combine two or more arrays into one, so you can more effectively manage and organize your data.

Ultimately, merging arrays can be a great way to save you time and prevent errors. 

If you’re ever in doubt when it comes to merging arrays, refer back to this guide for an easy-to-follow, step-by-step guide for merging arrays in JavaScript.