EC
TS2549
TypeScriptERRORNotableTypeHIGH confidence

Type 'X' is not an array type or a string type or does not have a '[Symbol.it...

Production Risk

Build will fail; resolve before shipping.

What this means

A type-checking error (TS2549): Type 'X' is not an array type or a string type or does not have a '[Symbol.iterator]()' method that returns an iterator.. This diagnostic is emitted by the TypeScript compiler when type 'X' is not an array type or a string type or does not have a '[Symbol.iterator]()' method that returns an iterator..

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

TypeScript compiler reports TS2549 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS2549
// Type 'X' is not an array type or a string type or does not have a '[Symbol.iterator]()' method that returns an iterator.

expected output

error TS2549: Type 'X' is not an array type or a string type or does not have a '[Symbol.iterator]()' method that returns an iterator.

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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