[Solved-4 Solutions] Insert an item into an array at a specific index - javascript tutorial
Problem:
How to insert an item into an array at a specific index ?
Solution 1:
arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's simply an insert).
In this example we will create an array and add an element to it into index 2:
var arr = [];
arr[0] = "Oscar Wilde";
arr[1] = "Kurt Vonnegut";
arr[2] = "Fyodor Dostoevsky";
arr[3] = "George Orwell";
arr[4] = "Ernest Hemingway";
console.log(arr.join());
arr.splice(2, 0, "Rowling");
console.log(arr.join());
The output of the code above will be:
Oscar Wilde,Kurt Vonnegut,Fyodor Dostoevsky,George Orwell,Ernest Hemingway Oscar Wilde,Kurt Vonnegut,Rowling,Fyodor Dostoevsky,George Orwell,Ernest Hemingway
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Insert an item into an arraySolution 2:
To implement the Array.insert method by doing this:
Array.prototype.insert = function ( index, item ) {
this.splice( index, 0, item );
};
Then we can use like this:
var arr = [ 'A', 'B', 'D', 'E' ];
arr.insert(2, 'C');
// => arr == [ 'A', 'B', 'C', 'D', 'E' ]Solution 3:
Here are two functions (insertAt, insertArrayAt) 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;
}
Here how to use the functions (insertAt, insertArrayAt):
// if we want to insert specific values whether constants or variables:
insertAt(arr, 1, "x", "y", "z");
// OR if we have an array:
var arrToInsert = ["x", "y", "z"];
insertArrayAt(arr, 1, arrToInsert);
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Unique values in an arraySolution 4:
Array.prototype.insert() is essential for functional programming. Actually splice could have been perfect if it had returned the mutated array instead of a totally meaningless empty array.
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>");
This Array.prototype.insert() method which doesn't mutate the original array.
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));