EC
TS1387
TypeScriptERRORNotableSyntaxHIGH confidence

Function type notation must be parenthesized when used in an intersection type.

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1387): Function type notation must be parenthesized when used in an intersection type.. This diagnostic is emitted by the TypeScript compiler when function type notation must be parenthesized when used in an intersection type..

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

TypeScript compiler reports TS1387 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1387
// Function type notation must be parenthesized when used in an intersection type.

expected output

error TS1387: Function type notation must be parenthesized when used in an intersection type.

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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