I’m not sure about more efficient in terms of big-O but certainly using the unshift
method is more concise:
var a = [1, 2, 3, 4];
a.unshift(0);
// => [0, 1, 2, 3, 4]
console.log({a});
[Edit]
This jsPerf benchmark shows that unshift
is decently faster in at least a couple of browsers, regardless of possibly different big-O performance if you are ok with modifying the array in-place. If you really can’t mutate the original array then you would do something like the below snippet, which doesn’t seem to be appreciably faster than your solution:
a.slice().unshift(0); // Use "slice" to avoid mutating "a".
[Edit 2]
For completeness, the following function can be used instead of OP’s example prependArray(...)
to take advantage of the Array unshift(...)
method:
function prepend(value, array) {
var newArray = array.slice();
newArray.unshift(value);
return newArray;
}
var x = [1, 2, 3];
var y = prepend(0, x);
// x => [1, 2, 3];
// y => [0, 1, 2, 3];
console.log({ x, y });