Hooks & effects in the React assessment

What it covers

useState, useEffect and the other built-in hooks, the rules of hooks, dependency arrays, cleanup and fetching data inside effects.

Topics in the practice set for this area

• hooks
• hooks / effects
• hook rules
• data fetching

How it is tested

In the timed assessment, questions in this area use these formats: code you write, matching, multiple choice, short answer. Each attempt draws its own set of questions, and this area gets its own sub-score on the credential when the attempt includes enough questions from it. The assessment questions themselves are never published; the practice set below is written separately for study.

What to practice

• Build a component that fetches data in an effect and cancels the request on unmount.
• Find the missing dependency in an effect and explain the bug it causes.
• Extract repeated logic into a custom hook.

Try a practice question

From the free practice set (6 questions in this area). Answers and explanations are in the practice set.

• React's useState hook returns:
• useEffect with `[]` dependency array runs:
• A component keeps a `setInterval` id so a Stop button can clear it later. Updating the id should not re-render anything. Where should the id live?

More React study guides

• How to Pass the Provyn React Assessment
• Rendering & state
• Performance & accessibility