JavaScript ReferenceError - variable is not defined Last Updated : 15 Jul, 2025 Comments Improve Suggest changes Like Article Like Report This JavaScript exception variable is not defined and occurs if there is a non-existent variable that is referenced somewhere. Message: ReferenceError: "x" is not defined Error Type: ReferenceError Cause of Error: There is a non-existent variable that is referenced somewhere in the script. That variable has to be declared or make sure the variable is available in the current script or scope. Example 1: In this example, the variable(val1) is being accessed from the outside of the function, So the error has not occurred. JavaScript function sum() { let val1 = 2; let val2 = 3; return val1 + val2; } console.log(val1); Output: ReferenceError: 'val1' is not defined Example 2: In this example, the variable(GFG) is not defined, So the error has occurred. JavaScript GFG.substring(2); Output: ReferenceError: 'GFG' is not defined Comment More infoAdvertise with us P PranchalKatiyar Follow Improve Article Tags : JavaScript Web Technologies JavaScript-Errors Explore JavaScript Tutorial 8 min read JavaScript BasicsIntroduction to JavaScript 4 min read JavaScript Versions 2 min read How to Add JavaScript in HTML Document? 3 min read JavaScript Syntax 6 min read JavaScript Output 4 min read JavaScript Comments 2 min read JS Variables & DatatypesVariables and Datatypes in JavaScript 6 min read Global and Local variables in JavaScript 4 min read JavaScript Let 6 min read JavaScript const 5 min read JavaScript Var Statement 7 min read JS OperatorsJavaScript Operators 5 min read Operator precedence in JavaScript 2 min read JavaScript Arithmetic Operators 5 min read JavaScript Assignment Operators 5 min read JavaScript Comparison Operators 5 min read JavaScript Logical Operators 5 min read JavaScript Bitwise Operators 5 min read JavaScript Ternary Operator 4 min read JavaScript Comma Operator 2 min read JavaScript Unary Operators 4 min read JavaScript in and instanceof operators 3 min read JavaScript String Operators 3 min read JS StatementsJavaScript Statements 4 min read JavaScript if-else 3 min read JavaScript switch Statement 4 min read JavaScript Break Statement 2 min read JavaScript Continue Statement 1 min read JavaScript Return Statement 4 min read JS LoopsJavaScript Loops 3 min read JavaScript For Loop 4 min read JavaScript While Loop 3 min read JavaScript For In Loop 3 min read JavaScript for...of Loop 3 min read JavaScript do...while Loop 4 min read JS Perfomance & DebuggingJavaScript | Performance 4 min read Debugging in JavaScript 4 min read JavaScript Errors Throw and Try to Catch 2 min read JS ObjectObjects in Javascript 4 min read Object Oriented Programming in JavaScript 3 min read JavaScript Objects 6 min read Creating objects in JavaScript 5 min read JavaScript JSON Objects 3 min read JavaScript Object Reference 4 min read JS FunctionFunctions in JavaScript 4 min read How to write a function in JavaScript ? 4 min read JavaScript Function Call 2 min read Different ways of writing functions in JavaScript 3 min read Difference between Methods and Functions in JavaScript 3 min read Explain the Different Function States in JavaScript 3 min read JavaScript Function Complete Reference 3 min read JS ArrayJavaScript Arrays 7 min read JavaScript Array Methods 7 min read Best-Known JavaScript Array Methods 6 min read Important Array Methods of JavaScript 7 min read JavaScript Array Reference 4 min read Like