TDZ 🟨 JavaScript

ReferenceError: Cannot access 'x' before initialization

A let/const/class was used before its declaration line ran (temporal dead zone) — often a circular import.

Seen on: JavaScript

Meaning

let/const exist from the start of the block but can’t be read until declared. In bundled apps the usual cause is two modules importing each other.

Common causes

  • Using a variable above its declaration
  • Circular imports between modules
  • Class used before its declaration

⚡ Quick fix

  1. Move the declaration up
  2. Break circular imports (extract shared code to a third module)
  3. Import lazily inside functions

Detailed fix by platform

JavaScript

  1. madge --circular src/ finds import cycles

How to diagnose

  1. Order — Declared before use?
  2. Imports — Any circular dependency?

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