EC
TS2860
TypeScriptERRORNotableTypeHIGH confidence

The left-hand side of an 'instanceof' expression must be assignable to the fi...

Production Risk

Build will fail; resolve before shipping.

What this means

A type-checking error (TS2860): The left-hand side of an 'instanceof' expression must be assignable to the first argument of the right-hand side's '[Symbol.hasInstance]' method.. This diagnostic is emitted by the TypeScript compiler when the left-hand side of an 'instanceof' expression must be assignable to the first argument of the right-hand side's '[Symbol.hasInstance]' method..

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

TypeScript compiler reports TS2860 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS2860
// The left-hand side of an 'instanceof' expression must be assignable to the first argument of the right-hand side's '[Symbol.hasInstance]' method.

expected output

error TS2860: The left-hand side of an 'instanceof' expression must be assignable to the first argument of the right-hand side's '[Symbol.hasInstance]' method.

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

Content generated with AI assistance and reviewed for accuracy. Found an error? hello@errcodes.dev

← All TypeScript errors