array.insert javascript

How can I insert an item into an array at a specific index?

stackoverflow.com › questions › 586182 › how-can-i-insert-an-item-into-an-array-at-a-specific-index

You want the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert).

In this example we will create an array and add an element to it into index 2:

var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";

console.log(arr.join()); // Jani,Hege,Stale,Kai Jim,Borge
arr.splice(2, 0, "Lene");
console.log(arr.join()); // Jani,Hege,Lene,Stale,Kai Jim,Borge

UPDATE (24 May 2024)

You can now use the toSpliced method which behaves just like splice, however it returns a new array without mutating the existing one.

You could update the previous example like so:

const updated = arr.toSpliced(2, 0, "Lene");

Answer from tvanfosson on Stack Overflow

MDN Web Docs

developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › Array › splice

Array.prototype.splice() - JavaScript | MDN

To create a new array with a segment removed and/or replaced without mutating the original array, use toSpliced(). To access part of an array without modifying it, see slice(). const months = ["Jan", "March", "April", "June"]; months.splice(1, 0, "Feb"); // Inserts at index 1 console.log(months); // Expected output: Array ["Jan", "Feb", "March", "April", "June"] months.splice(4, 1, "May"); // Replaces 1 element at index 4 console.log(months); // Expected output: Array ["Jan", "Feb", "March", "April", "May"]

Stack Overflow

stackoverflow.com › questions › 586182 › how-can-i-insert-an-item-into-an-array-at-a-specific-index

javascript - How can I insert an item into an array at a specific index? - Stack Overflow

Top answer

1 of 16

6880

You want the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert).

In this example we will create an array and add an element to it into index 2:

var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";

console.log(arr.join()); // Jani,Hege,Stale,Kai Jim,Borge
arr.splice(2, 0, "Lene");
console.log(arr.join()); // Jani,Hege,Lene,Stale,Kai Jim,Borge

UPDATE (24 May 2024)

You can now use the toSpliced method which behaves just like splice, however it returns a new array without mutating the existing one.

You could update the previous example like so:

const updated = arr.toSpliced(2, 0, "Lene");

2 of 16

427

You can implement the Array.insert method by doing this:

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

Then you can use it like:

var arr = [ 'A', 'B', 'E' ];
arr.insert(2, 'C', 'D');

// => arr == [ 'A', 'B', 'C', 'D', 'E' ]

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