EC
TS1139
TypeScriptERRORNotableSyntaxHIGH confidence

Type parameter declaration expected.

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1139): Type parameter declaration expected.. This diagnostic is emitted by the TypeScript compiler when type parameter declaration expected..

Why it happens
  1. 1Incorrect number or type of generic type arguments
How to reproduce

TypeScript compiler reports TS1139 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1139
// Type parameter declaration expected.

expected output

error TS1139: Type parameter declaration expected.

Fix

Address the TypeScript diagnostic

WHEN When this error is reported by the compiler

Address the TypeScript diagnostic
// Run the TypeScript compiler for details:
npx tsc --noEmit
// Use the TypeScript playground to test your code:
// https://www.typescriptlang.org/play

Why this works

Review the full error message and location; the TypeScript handbook provides guidance on each error category.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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