EC
TS1244
TypeScriptERRORNotableSyntaxHIGH confidence

Abstract methods can only appear within an abstract class.

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1244): Abstract methods can only appear within an abstract class.. This diagnostic is emitted by the TypeScript compiler when abstract methods can only appear within an abstract class..

Why it happens
  1. 1A concrete class extends an abstract class but does not implement all abstract members
How to reproduce

TypeScript compiler reports TS1244 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1244
// Abstract methods can only appear within an abstract class.

expected output

error TS1244: Abstract methods can only appear within an abstract 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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