JavaScript TypeError - "X" is read-only Last Updated : 22 May, 2023 Comments Improve Suggest changes Like Article Like Report This JavaScript exception is read-only works in strict mode-only and It occurs if a global variable or object property which has assigned to a value, is a read-only property. Message: TypeError: Assignment to read-only properties is not allowed in strict mode (Edge) TypeError: "x" is read-only (Firefox) TypeError: 0 is read-only (Firefox) TypeError: Cannot assign to read only property 'x' of #<Object> (Chrome) TypeError: Cannot assign to read only property '0' of [object Array] (Chrome) Error Type: TypeError Cause of Error: The global variable or object property that has assigned value is a read-only property. You can not write data in those variables. Example 1: In this example, any property of GFG_Obj can not be modified. JavaScript 'use strict'; let GFG_Obj = Object.freeze({ prop1: 'val1', prop2: 'val2' }); GFG_Obj.prop2 = 0; // TypeError Output(in console): TypeError: Assignment to read-only properties is not allowed in strict mode Example 2: In this example, the value of Math.PI can not be changed(Which is read-only). JavaScript 'use strict'; Math.PI = 5; Output(in console): TypeError: Assignment to read-only properties is not allowed in strict mode 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