How to Add New Array Elements at the Beginning of an Array in JavaScript

How can I add new array elements at the beginning of an array in JavaScript?

Use unshift. It's like push, except it adds elements to the beginning of the array instead of the end.

unshift/push - add an element to the beginning/end of an array
shift/pop - remove and return the first/last element of an array

A simple diagram...

   unshift -> [array] <- push
   shift   <- [array] -> pop

and chart:

          add  remove  start  end
   push    X                   X
    pop           X            X
unshift    X             X
  shift           X      X

Check out the MDN Array documentation. Virtually every language that has the ability to push/pop elements from an array will also have the ability to unshift/shift (sometimes called push_front/pop_front) elements, you should never have to implement these yourself.

As pointed out in the comments, if you want to avoid mutating your original array, you can use concat, which concatenates two or more arrays together. You can use this to functionally push a single element onto the front or back of an existing array; to do so, you need to turn the new element into a single element array:

const array = [3, 2, 1]

const newFirstElement = 4

const newArray = [newFirstElement].concat(array) // [ 4, 3, 2, 1 ]

console.log(newArray);

js: add element at the start of an array

Ok,

let arr = [1,2]
let foo={bar:true}
arr=[foo].concat(arr)

also what you already know works

arr=[foo, ...arr]

That's it

How to insert an item into an array at a specific index (JavaScript)

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

Copy array items into another array

Use the concat function, like so:

var arrayA = [1, 2];
var arrayB = [3, 4];
var newArray = arrayA.concat(arrayB);

The value of newArray will be [1, 2, 3, 4] (arrayA and arrayB remain unchanged; concat creates and returns a new array for the result).

javascript pushing element at the beginning of an array

Use unshift, which modifies the existing array by adding the arguments to the beginning:

TheArray.unshift(TheNewObject);

How to append something to an array?

Use the Array.prototype.push method to append values to the end of an array:

// initialize array
var arr = [
  "Hi",
  "Hello",
  "Bonjour"
];

// append new value to the array
arr.push("Hola");

console.log(arr);

How to append new array to beginning of multi-dimensional array

Here you go with the solution https://jsfiddle.net/fkz9ubug/

var vArr = [[1, 1], [2, 3], [3, 3]];var newv = [4, 4];vArr.unshift(newv)
console.log(vArr);

How to extend an existing JavaScript array with another array, without creating a new array

The .push method can take multiple arguments. You can use the spread operator to pass all the elements of the second array as arguments to .push:

>>> a.push(...b)

If your browser does not support ECMAScript 6, you can use .apply instead:

>>> a.push.apply(a, b)

Or perhaps, if you think it's clearer:

>>> Array.prototype.push.apply(a,b)

Please note that all these solutions will fail with a stack overflow error if array b is too long (trouble starts at about 100,000 elements, depending on the browser).

If you cannot guarantee that b is short enough, you should use a standard loop-based technique described in the other answer.

Adding text to beginning of each array element

for(var i=0;i<array.length;i++){
    array[i]="#"+array[i];
}