FrontendHaltReact·Intermediate·Coding·1 min read
What warning does React give when an input switches between controlled and uncontrolled?
Short interview answer
It warns that a component is changing an uncontrolled input to be controlled, or vice versa, typically because the value prop starts as undefined and later becomes a defined string, or the reverse — React expects one model to be chosen and kept consistent.
Example
// value is undefined on first render -> becomes a string later => warning<input value={user?.name} onChange={onChange} />// Fix: <input value={user?.name ?? ''} ... />Key takeaway
Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.