Popular:
 Building Resilient Systems on AWS: Learn how to design and implement a resilient, highly available, fault-tolerant infrastructure on AWS.

Array: Insert an Item at a Specific Index with JavaScript

By  on  

There are many tasks related to arrays that sound quite simple but (1) aren't and (2) aren't required of a developer very often. I was encountered with one such task recently: inserting an item into an existing array at a specific index. Sounds easy and common enough but it took some research to figure it out.

// The original array
var array = ["one", "two", "four"];
// splice(position, numberOfItemsToRemove, item)
array.splice(2, 0, "three");

array;  // ["one", "two", "three", "four"]

If you aren't adverse to extending natives in JavaScript, you could add this method to the Array prototype:

Array.prototype.insert = function (index, item) {
  this.splice(index, 0, item);
};

I've tinkered around quite a bit with arrays, as you may have noticed:

Arrays are super useful -- JavaScript just makes some tasks a bit more ... code-heavy than they need to be. Keep these snippets in your toolbox for the future!

Request Metrics real user monitoring
Request Metrics real user monitoring
Request Metrics real user monitoring
Request Metrics real user monitoring

Recent Features

  • By
    7 Essential JavaScript Functions

    I remember the early days of JavaScript where you needed a simple function for just about everything because the browser vendors implemented features differently, and not just edge features, basic features, like addEventListener and attachEvent.  Times have changed but there are still a few functions each developer should...

  • By
    CSS Filters

    CSS filter support recently landed within WebKit nightlies. CSS filters provide a method for modifying the rendering of a basic DOM element, image, or video. CSS filters allow for blurring, warping, and modifying the color intensity of elements. Let's have...

Incredible Demos

  • By
    CSS content and attr

    CSS is becoming more and more powerful but in the sense that it allows us to do the little things easily.  There have been larger features added like transitions, animations, and transforms, but one feature that goes under the radar is generated content.  You saw a...

  • By
    Jack Rugile’s Favorite CodePen Demos

    CodePen is an amazing source of inspiration for code and design. I am blown away every day by the demos users create. As you'll see below, I have an affinity toward things that move. It was difficult to narrow down my favorites, but here they are!

Discussion

  1. Aram Koukia

    Man, isn’t this JavaScript powerful…

  2. MaxArt

    How about a little step further? Since splice takes an indefinite number of arguments, you can do something like this:

    Array.prototype.insert = function (index) {
  this.splice.apply(this, [index, 0].concat(this.slice.call(arguments, 1)));
};

    so you can do

    array.insert(2, "three", "another three", "the last three");
array;  // ["one", "two", "three", "another three", "the last three", "four"]
  3. Mahdi

    Great tip, thanks. I knew this trick before but I forgot that splice could take more than 2 arguments, phew.

  4. Filip

    Yes, it’s a very useful function. Last year I was delighted to find out that it exists – it made the project I was working on extremely useful.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!