A page parses a 30 MB CSV the user drops in, validates every row, and renders a preview. Should that go in a web worker? Talk me through the decision and the implementation.
Answer it out loud before you open anything. The value of the flags below is in comparing them to what you actually said.
The situation behind the question
A data import tool. Today the whole thing runs in the drop handler; the tab freezes and users think it crashed. A previous attempt to move it to a worker was abandoned because "it was not any faster".
What it is really testing
Whether the candidate knows what a worker buys and what it costs. The abandoned attempt is the discriminator: a worker does not make CPU work faster, it makes it not block the main thread, and someone who measured total time concluded correctly that nothing improved.