EC
TS6666
TypeScriptERRORNotableConfigHIGH confidence

Ensure overriding members in derived classes are marked with an override modi...

Production Risk

Build will fail; resolve before shipping.

What this means

A compiler configuration error (TS6666): Ensure overriding members in derived classes are marked with an override modifier.. This diagnostic is emitted by the TypeScript compiler when ensure overriding members in derived classes are marked with an override modifier..

Why it happens
  1. 1Incorrect TypeScript syntax or type usage
  2. 2Type mismatch between declared and actual value
How to reproduce

TypeScript compiler reports TS6666 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS6666
// Ensure overriding members in derived classes are marked with an override modifier.

expected output

error TS6666: Ensure overriding members in derived classes are marked with an override modifier.

Fix

Implement all abstract members

WHEN Extending an abstract class

Implement all abstract members
abstract class Base {
  abstract doWork(): void;
}
class Derived extends Base {
  doWork(): void { /* implementation */ }
}

Why this works

All abstract members must be implemented in concrete subclasses.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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