Get confident with React Compiler vocabulary — auto-memoization, compiler rules, opt-out directives, and debugging output.
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During standup, a React dev mentions the team is evaluating React Compiler (React Forget). What is it?
React Compiler (formerly React Forget) is a Babel/SWC plugin that analyses component code at build time and inserts memoization automatically. It understands React's data flow model and only memoizes what actually needs it — eliminating the cognitive overhead of manual useMemo/useCallback/memo.
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In a PR review, you see "use no memo" at the top of a component. What does this directive do?
"use no memo" is a compiler opt-out directive. Place it at the top of a component or hook file to tell React Compiler to leave that scope untouched. This is useful during migration when a component has patterns the compiler can't safely analyse, or when you need to preserve specific manual memoization behaviour.
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An incident reveals that React Compiler is skipping a component silently. What causes the compiler to bail out?
React Compiler requires strict adherence to the Rules of React. If a component mutates props, performs side effects during render, or calls hooks conditionally, the compiler detects the violation and skips that component entirely — emitting a diagnostic. Running npx react-compiler-healthcheck shows which components are bailed out and why.
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In a design review, the team asks how React Compiler handles auto-memoization of derived values. How does it work?
React Compiler performs static analysis to determine which computed values depend on which inputs. It then inserts memoization automatically — only recomputing a value when its inputs change. This is semantically equivalent to useMemo with a correct dependency array, but without the developer needing to maintain that array manually.
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During a code review, someone mentions react-compiler-healthcheck. What does this tool do?
npx react-compiler-healthcheck scans your codebase statically and produces a report: how many components would be optimised, how many would be skipped, and the specific reasons for each bail-out. Run it before enabling React Compiler in production to understand the impact and fix any Rules of React violations.