How to add new array element at the start of an array in javascript?

Unshift and Shift are the functions which can be used to add or remove elements from the array starting point, while Push and pop are the functions which is used to add element or remove relement at the end of the array

so basically what you need is

var a = [12, 24, 50, 100]; //this is your array
a.unshift(11); // add element add the start of an array
console.log(a); // this will be your result [11,12, 24, 50, 100]

here is a simple diagram created by me

hope the aboave helps to understand functions to add or remove elements from arrays in javascript

The above answer works well, but I think it is better to use Javascript .splice() method, which is used to add/remove items from an array, here is the example of it.

var arr = [12, 30, 34, 55];
arr.splice(0, 0, 11);
console.log(arr);

Output of above will give arr value as below

[
  11,
  12,
  20,
  34,
  55
]

If you want to understand array.splice method, here is it's syntax

array.splice(PositionToAddRemoveItems, HowManyItemsToRemove, Item1ToAdd, ....., ItemXtoAdd)

So basically, that's why we used arr.splice(0, 0, 11);

to add item a 0th (1st) position,

0 elements to remove

and added new item with value '11'.