Group by key in JavaScript

Turns a flat array into an object keyed by whatever you pick out of each item.

function groupBy(items, keyFn) {
  const groups = {};
  for (const item of items) {
    const key = keyFn(item);
    if (!groups[key]) groups[key] = [];
    groups[key].push(item);
  }
  return groups;
}

Keywords and builtins used here

• const
• for
• function
• if
• of
• return

The run, in numbers

Lines

9

Characters to type

183

Tokens

61

Three-star pace

95 tpm

At the three-star pace of 95 tokens a minute, this run takes about 39 seconds.

Type this snippet

Step 5 of 8 in Objects & collections, step 31 of 43 in Language basics.

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