js: add element at the start of an array [duplicate]

Question

Let´s say I have this array: let array = ["somevalue", "anothervalue"]
So what I wanted to da was to add a value, for example: let foo = {bar: true} and add this value at index 0, but not overwrite the old value, rather kind of 'push' the rest of the values back. I´ve heard of array = [foo, ...array] but I am not quite sure what it does and how and when to use it.
Anyone any ideas?

Answer 1

let array = ["somevalue", "anothervalue"]
let foo = {bar: true}
array.unshift(foo);
console.log(array); // prints [{bar: true}, "somevalue", "anothervalue"]

Similarly, the shift() method removes the first item in the array.

Answer 2

It simply append the foo in front of array. so array will become

[{bar: true}, "somevalue", "anothervalue"]

Alternate :

You can also use unshift, it also append data at index 0, eg.

let array = [2, 3, 4]
array.unshift(1)
console.log(array) /// output : [1, 2, 3, 4]

Answer 3

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