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 arrayshift
/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);
concat
can also append items. The arguments to concat
can be of any type; they are implicitly wrapped in a single-element array, if they are not already an array:
const array = [3, 2, 1]
const newLastElement = 0
// Both of these lines are equivalent:
const newArray1 = array.concat(newLastElement) // [ 3, 2, 1, 0 ]
const newArray2 = array.concat([newLastElement]) // [ 3, 2, 1, 0 ]
console.log(newArray1);
console.log(newArray2);
With ES6, use the spread operator ...
:
Demo
var arr = [23, 45, 12, 67];
arr = [34, ...arr]; // RESULT : [34,23, 45, 12, 67]
console.log(arr)
var a = [23, 45, 12, 67];
a.unshift(34);
console.log(a); // [34, 23, 45, 12, 67]