JS Array Prototype Unshift - thelastmile/FreeCodeCamp GitHub Wiki
JavaScript Array.prototype.unshift()
The JavaScript array method .unshift()
adds one or more elements to the beginning of an array and returns the new length of the array.
Syntax
arr.unshift([element1[, ...[, elementN]]])
Parameters
The elements to add to the front of the array.
Returns
The new length
of the array upon which the method was called.
Examples
var array = [1, 2, 3, 4, 5];
array.unshift(0);
// If we console.log(array.shift()); the console would output 6.
// array is now [0, 1, 2, 3, 4, 5];
array.unshift([-1]);
// array is now [[-1], 0, 1, 2, 3, 4, 5];
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Source MDN