JavaScript drills

The one-liners a live coding round expects me to type without thinking, and the ones I still fumble under a timer. A short refresher per method, then exercises checked in a sandbox against hidden cases. Solved marks stay in this browser; nothing leaves it.

• map

  Transform every item. Same length, new array.

  5 exercises 0 / 5
• filter

  Keep the items that pass a test. Same items, fewer of them.

  6 exercises 0 / 6
• reduce

  Fold a list into one value: a number, an object, or a new list.

  6 exercises 0 / 6
• find, some, every

  Ask a question about a list without building a new one.

  6 exercises 0 / 6
• sort

  Order a copy of the list with a comparator you control.

  5 exercises 0 / 5

28 exercises across 5 lessons. reset progress