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JavaScript variable or symbol is not defined

ReferenceError: "x" is not defined

JavaScript tried to use a variable, function, or imported name that does not exist in the current scope.

ReferenceError: x is not definedruntime

Observed message

ReferenceError: "x" is not defined

Why it happens

  • The symbol was never declared or imported.
  • A script or module load order issue means the value is used too early.
  • A typo or refactor changed the variable or function name.

How to fix it

  1. Check spelling and confirm the symbol is declared or imported in scope.
  2. Verify scripts, modules, and dependencies load before the symbol is used.
  3. Use linters or types to catch missing references earlier.

Official reference

MDN: ReferenceError: x is not defined

Related errors

ReferenceError: can't access lexical declaration before initializationJavaScript accessed a let or const binding before initializationReferenceError: assignment to undeclared variableJavaScript assigned to an undeclared variableTypeError: class constructors must be invoked with 'new'JavaScript class constructor was called without newRangeError: x can't be converted to BigInt because it isn't an integerJavaScript could not convert a non-integer value to BigInt

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JavaScript x is not defined: causes and fixes | Error Atlas