Adds values to the start.
Alternatives: unshift, unshift$.
Similar: push, pop, shift, unshift.
This is part of package extra-array.
array.unshift$(x, ...vs);
// x: an array (updated)
// vs: values to add
// → x
const array = require("extra-array");
var x = [3, 4];
array.unshift$(x, 2);
// [ 2, 3, 4 ]
x;
// [ 2, 3, 4 ]
var x = [3, 4];
array.unshift$(x, 1, 2);
// [ 1, 2, 3, 4 ]