How to insert an item into an array at a specific index (JavaScript)?
How to insert an item into an array at a specific index (JavaScript)?
Question
I am looking for a JavaScript array insert method, in the style of:
arr.insert(index, item)
Preferably in jQuery, but any JavaScript implementation will do at this point.
Accepted Answer
What you want is 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());
arr.splice(2, 0, "Lene");
console.log(arr.join());
Read more... Read less...
You can implement the Array.insert
method by doing this:
Array.prototype.insert = function ( index, item ) {
this.splice( index, 0, item );
};
Then you can use it like:
var arr = [ 'A', 'B', 'D', 'E' ];
arr.insert(2, 'C');
// => arr == [ 'A', 'B', 'C', 'D', 'E' ]
Other than splice, you can use this approach which will not mutate the original array, but will create a new array with the added item. You should usually avoid mutation whenever possible. I'm using ES6 spread operator here.
const items = [1, 2, 3, 4, 5]
const insert = (arr, index, newItem) => [
// part of the array before the specified index
...arr.slice(0, index),
// inserted item
newItem,
// part of the array after the specified index
...arr.slice(index)
]
const result = insert(items, 1, 10)
console.log(result)
// [1, 10, 2, 3, 4, 5]
This can be used to add more than one item by tweaking the function a bit to use the rest operator for the new items, and spread that in the returned result as well
const items = [1, 2, 3, 4, 5]
const insert = (arr, index, ...newItems) => [
// part of the array before the specified index
...arr.slice(0, index),
// inserted items
...newItems,
// part of the array after the specified index
...arr.slice(index)
]
const result = insert(items, 1, 10, 20)
console.log(result)
// [1, 10, 20, 2, 3, 4, 5]
Custom array insert
methods
1. With multiple arguments and chaining support
/* Syntax:
array.insert(index, value1, value2, ..., valueN) */
Array.prototype.insert = function(index) {
this.splice.apply(this, [index, 0].concat(
Array.prototype.slice.call(arguments, 1)));
return this;
};
It can insert multiple elements (as native splice
does) and supports chaining:
["a", "b", "c", "d"].insert(2, "X", "Y", "Z").slice(1, 6);
// ["b", "X", "Y", "Z", "c"]
2. With array-type arguments merging and chaining support
/* Syntax:
array.insert(index, value1, value2, ..., valueN) */
Array.prototype.insert = function(index) {
index = Math.min(index, this.length);
arguments.length > 1
&& this.splice.apply(this, [index, 0].concat([].pop.call(arguments)))
&& this.insert.apply(this, arguments);
return this;
};
It can merge arrays from the arguments with the given array and also supports chaining:
["a", "b", "c", "d"].insert(2, "V", ["W", "X", "Y"], "Z").join("-");
// "a-b-V-W-X-Y-Z-c-d"
If you want to insert multiple elements into an array at once check out this Stack Overflow answer: A better way to splice an array into an array in javascript
Also here are some functions to illustrate both examples:
function insertAt(array, index) {
var arrayToInsert = Array.prototype.splice.apply(arguments, [2]);
return insertArrayAt(array, index, arrayToInsert);
}
function insertArrayAt(array, index, arrayToInsert) {
Array.prototype.splice.apply(array, [index, 0].concat(arrayToInsert));
return array;
}
Finally here is a jsFiddle so you can see it for youself: http://jsfiddle.net/luisperezphd/Wc8aS/
And this is how you use the functions:
// if you want to insert specific values whether constants or variables:
insertAt(arr, 1, "x", "y", "z");
// OR if you have an array:
var arrToInsert = ["x", "y", "z"];
insertArrayAt(arr, 1, arrToInsert);
For proper functional programming and chaining purposes an invention of Array.prototype.insert()
is essential. Actually splice could have been perfect if it had returned the mutated array instead of a totally meaningless empty array. So here it goes
Array.prototype.insert = function(i,...rest){
this.splice(i,0,...rest)
return this
}
var a = [3,4,8,9];
document.write("<pre>" + JSON.stringify(a.insert(2,5,6,7)) + "</pre>");
Well ok the above with the Array.prototype.splice()
one mutates the original array and some might complain like "you shouldn't modify what doesn't belong to you" and that might turn out to be right as well. So for the public welfare i would like to give another Array.prototype.insert()
which doesn't mutate the original array. Here it goes;
Array.prototype.insert = function(i,...rest){
return this.slice(0,i).concat(rest,this.slice(i));
}
var a = [3,4,8,9],
b = a.insert(2,5,6,7);
console.log(JSON.stringify(a));
console.log(JSON.stringify(b));