4 JavaScript Array methods you didn't know you needed

Patrick Brosset - May 12, 2022

The Array JavaScript built-in object comes with a lot of methods that make manipulating arrays easy. I often forget about them and end up writing code with complicated for loops that could have been done in much simpler ways.

So here are 4 methods available to JavaScript Arrays that might help you too.

Get the last item in an array

Have you ever done myList[myList.length - 1] to get the last item in the myList array?

If so, it just got a lot easier with the Array.at method. This method takes an single integer argument that indicates which item you want in the array, and a negative number will count back from the last item.

➡️ const lastItem = myList.at(-1);

Array.at is supported in all browser engines, as well as Node.js and Deno.

Flatten an array of arrays

The Array.flat method creates a new array from the values contained in an array of arrays.

➡️ const list = [0, 1, [2, 3], [4, 5]].flat(); // [0, 1, 2, 3, 4, 5]

The method also takes an optional argument to specify the depth at which the recursive flattening should stop. So flattening this 3 level deep array for example will require passing 3 as an argument to the method:

➡️ const list = [0, [1, [2, [3]]]].flat(3); // [0, 1, 2, 3]

Array.flat is also supported in all browsers, as well as Node.js and Deno.

Test an array's values

Sometimes you need to check that at least 1 item in an array matches some condition. You can write a for loop to do it:

let doesItHaveTheValueINeed = false;
for (const item of myList) {
  if (condition(item)) {
    doesItHaveTheValueINeed = true;
    break;
  }
}

Or, use the Array.some method instead!

➡️ myList.some(condition);

The very similar Array.every method is also interesting here. It works the same but tests if all items in the array match the condition.

➡️ myList.every(condition);

Support for both some and every is green all across the board too.

Get the iteration index in a for..of loop

This last method is Array.entries which makes this useful tip possible: getting the current iteration index even when using a for..of loop.

for..of loops are great to make your code simpler to write and read:

// 😒
for (let i = 0; i < myList.length; i++) {
  const item = myList[i];
}

// 😃
for (const item of myList){
  ...
}

However the second, more compact, for loop does not have access to the current iteration index, which the first for loop does. Here's how to get it:

➡️ for (const [index, item] of myList.entries()) { ... }

The Array.entries method returns an iterator that provides access to the key and value of each item in the array.

Support for entries is green all across the board too.

That's it for this short blog post. I hope these methods come in handy at some point!