Iterate an array as a pair (current, next) in JavaScript

Question

In the question Iterate a list as pair (current, next) in Python, the OP is interested in iterating a Python list as a series of current, next pairs. I have th

Answer 1

Here's my approach, using Array.prototype.shift:

Array.prototype.pairwise = function (callback) {
    const copy = [].concat(this);
    let next, current;

    while (copy.length) {
        current = next ? next : copy.shift();
        next = copy.shift();
        callback(current, next);
    }
};

This can be invoked as follows:

// output:
1 2
2 3
3 4
4 5
5 6

[1, 2, 3, 4, 5, 6].pairwise(function (current, next) {
    console.log(current, next);
});

So to break it down:

while (this.length) {

Array.prototype.shift directly mutates the array, so when no elements are left, length will obviously resolve to 0. This is a "falsy" value in JavaScript, so the loop will break.

current = next ? next : this.shift();

If next has been set previously, use this as the value of current. This allows for one iteration per item so that all elements can be compared against their adjacent successor.

The rest is straightforward.