Array iteration patterns

The patterns you will use forever

Most array work reduces to a handful of loop shapes you already met in Python. Here they are in JavaScript, using the for...of loop from lesson 3-3.

Sum (Python's sum(xs) has no built-in here):

let total = 0;
for (const s of scores) {
  total = total + s;
}

Biggest so far:

let best = scores[0];
for (const s of scores) {
  if (s > best) best = s;
}

Count matches: start a counter at 0 and add 1 inside an if.

When the body is a single statement, the braces may be dropped, as in if (s > best) best = s;. In unit 7 you will replace several of these hand-written loops with one-liners like reduce, but the loop versions must feel easy first.