Generators in JavaScript

Functions that yield a stream of values lazily.

function* idMaker(start = 1) {
  let id = start;
  while (true) {
    yield id++;
  }
}

function* take(iterable, n) {
  let i = 0;
  for (const value of iterable) {
    if (i++ >= n) return;
    yield value;
  }
}

const ids = [...take(idMaker(100), 3)];

How it works

1. function* and yield produce values on demand.
2. An infinite generator is safe when consumed lazily.
3. Spreading a generator collects what it yields.

Keywords and builtins used here

• const
• for
• function
• if
• let
• of
• return
• while
• yield

The run, in numbers

Lines

16

Characters to type

231

Tokens

77

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 44 seconds.

Type this snippet

Step 1 of 2 in Generators, step 10 of 16 in Functions & patterns.

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