← Array methods are eager. Iterator helpers are lazy. Here's why that matters.Quiz
Eager arrays vs. lazy iterator helpers
Array methods like .filter() and .map() are eager: they run immediately and allocate a new intermediate array at each step. Iterator helpers run the same pipeline lazily, pulling one element at a time and stopping early. These questions check what lazy actually means, which methods trigger evaluation, when iterators beat arrays, and the one-shot gotcha that catches people.
questions8
pass mark70%
resultsat the end
No account needed. Answer all 8 questions, then see your score with every answer explained and a reference to the spec or MDN — pass and you can claim a certificate.