Array.prototype.unshift()

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.

elementN

The elements to add to the front of the arr.

The new length property of the object upon which the method was called.

The unshift method inserts the given values to the beginning of an array-like object.

unshift is intentionally generic. This method can be called or applied to objects resembling arrays. Objects which do not contain a length property—reflecting the last in a series of consecutive, zero-based numerical properties—may not behave in any meaningful manner.

Please note that, if multiple elements are passed as parameters, they're inserted in chunk at the beginning of the object, in the exact same order they were passed as parameters. Hence, calling unshift with n arguments once, or calling it n times with 1 argument (with a loop, for example), don't yield the same results.

See example:

let arr = [4, 5, 6]

arr.unshift(1, 2, 3)
console.log(arr);
// [1, 2, 3, 4, 5, 6]

arr = [4, 5, 6] // resetting the array

arr.unshift(1)
arr.unshift(2)
arr.unshift(3)

console.log(arr)
// [3, 2, 1, 4, 5, 6]

• Array.prototype.push()
• Array.prototype.pop()
• Array.prototype.shift()
• Array.prototype.concat()