EC
TS4112
TypeScriptERRORNotableDeclarationHIGH confidence

This member cannot have an 'override' modifier because its containing class '...

Production Risk

Build will fail; resolve before shipping.

What this means

A declaration emit error (TS4112): This member cannot have an 'override' modifier because its containing class 'X' does not extend another class.. This diagnostic is emitted by the TypeScript compiler when this member cannot have an 'override' modifier because its containing class 'X' does not extend another class..

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

TypeScript compiler reports TS4112 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS4112
// This member cannot have an 'override' modifier because its containing class 'X' does not extend another class.

expected output

error TS4112: This member cannot have an 'override' modifier because its containing class 'X' does not extend another class.

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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