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Array: Insert an Item at a Specific Index with JavaScript

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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!

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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.

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