typescript function_error ai_generated true

TS2394: This overload signature is not compatible with its implementation signature

ID: typescript/ts-overload-signature-error

Also available as: JSON · Markdown
88%Fix Rate
90%Confidence
50Evidence
2023-01-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
5 active — — —

Root Cause

The implementation signature must be compatible with all overload signatures. It must accept a superset of all parameter types.

generic

Workarounds

  1. 92% success Ensure the implementation signature accepts all overload parameter types 
    function parse(input: string): Document;
function parse(input: Buffer): Document;
function parse(input: string | Buffer): Document {
  // implementation handles both types
  const text = typeof input === 'string' ? input : input.toString();
  return parseDocument(text);
}

    Sources: https://www.typescriptlang.org/docs/handbook/2/functions.html#function-overloads

  2. 85% success Use a union type in the implementation for return types 
    function getValue(key: 'name'): string;
function getValue(key: 'age'): number;
function getValue(key: 'name' | 'age'): string | number {
  // implementation return type is union of all overload returns
}

    Sources: https://www.typescriptlang.org/docs/handbook/2/functions.html#overload-signatures-and-the-implementation-signature

Dead Ends

Common approaches that don't work:

  1. Make each overload signature identical to the implementation 65% fail

    Defeats the purpose of overloads; overloads should provide narrower type signatures for callers

Error Chain

Leads to:
Preceded by:
Frequently confused with: