TypeScript
TypeScript detected a variable used before being assigned
error TS2454: Variable 'X' is used before being assigned.
TypeScript found code that reads from a variable before every control path guarantees an assignment.
Error AtlasError Documentation and ResolutionObserved message
error TS2454: Variable 'X' is used before being assigned.
Why it happens
- A variable is declared without an initializer and read before all paths assign it.
- Conditional logic makes assignment uncertain from TypeScript's control-flow analysis.
- A refactor moved the read earlier than the guaranteed assignment point.
How to fix it
- Initialize the variable at declaration if that matches the intended behavior.
- Restructure the control flow so assignment always happens before the variable is read.
- Use a union with undefined only if an uninitialized state is genuinely valid.
Official reference
TypeScript Docs: Variable DeclarationsRelated errors
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