React Hooks
Also written as Hooks, useEffect, useState, Custom Hooks
The standard way to give React components memory and side effects (like fetching data) since 2019, replacing the older class-based style. useState and useEffect are the two everyone uses; custom hooks package reusable logic.
Think of it like
Clip-on attachments for a power tool: add exactly the capability a component needs instead of buying a heavier tool.
Junior or senior?
Every current React developer uses hooks, so the name alone says little.
Senior sounds like
Can explain a bug caused by useEffect (infinite loops, stale values) and has written their own custom hooks.
Ask them
“Tell me about a bug you hit with useEffect. What caused it and how did you fix it?”
Sounds like real experience
Names a concrete useEffect problem, such as an infinite re-render, a stale value, or a missing cleanup, and explains the fix in their own words.
Probe further if
Can only list hook names (useState, useEffect) without ever describing a problem they caused or solved.