Optimizing Re-renders in React Native: React.memo, useCallback, useMemo — When They Actually Help

React.memo, useCallback, and useMemo are the most misunderstood performance tools in React Native. Most developers either ignore them entirely and wonder why their lists re-render constantly, or wrap everything in all three and wonder why their app feels slower than before. Neither approach is right. This post covers what these tools actually do at the mechanics level, the most common ways they are misused, how to measure whether they are genuinely helping, and how to know when not to use them at all. What Re-renders Actually Are Before optimising re-renders, you need to be precise about what a re-render is and what it costs. A re-render in React means the component function runs again. React calls your function, gets a new JSX tree, diffs it against the previous one, and applies only the changes to the native view layer. The function running again does not necessarily mean anything visible changes on screen. The cost of a re-render has two parts. First, the cost of running the functio