JavaScript ReferenceError - Invalid assignment left-hand side

Last Updated : 15 Jul, 2025

This JavaScript exception invalid assignment left-hand side occurs if there is a wrong assignment somewhere in code. A single “=” sign instead of “==” or “===” is an Invalid assignment.

Message:

ReferenceError: invalid assignment left-hand side

Error Type:

ReferenceError

Cause of the error: There may be a misunderstanding between the assignment operator and a comparison operator.

Basic Example of ReferenceError - Invalid assignment left-hand side, run the code and check the console

Example 1:

JavaScript

if (Math.PI = 10 || Math.PI = 5) { console.log("Inside Loop"); }

Output:

ReferenceError: Invalid left-hand side in assignment

Example 1: In this example, “=” operator is misused as “==”, So the error occurred.

HTML

<!DOCTYPE html> <html lang="en"> <head> <title>Document</title> </head> <body style="text-align: center;"> <h1 style="color: green;"> GeeksforGeeks </h1> <p> JavaScript ReferenceError - Invalid assignment left-hand side </p> <button onclick="Geeks();"> click here </button> <p id="GFG_DOWN"></p> <script>  let el_down = document.getElementById("GFG_DOWN");  function Geeks() {  try {  if ((Math.PI = 10 || Math.PI = 5)) {  document.write("Inside Loop");  }  el_down.innerHTML =  "'Invalid assignment left-hand side'" +  " error has not occurred";  } catch (e) {  el_down.innerHTML =  "'Invalid assignment left-hand side'" +  "error has occurred";  }  }  </script> </body> </html>

Output:

JavaScript ReferenceError - Invalid assignment left-hand side

Example 2: In this example, the + operator is used with the declaration, So the error has not occurred.

HTML

<!DOCTYPE html> <html lang="en"> <head> <title>Invalid assignment left-hand side</title> </head> <body style="text-align:center;"> <h1 style="color:green;"> GeeksforGeeks </h1> <p> JavaScript ReferenceError - Invalid assignment left-hand side </p> <button onclick="Geeks();"> click here </button> <p id="GFG_DOWN"> </p> <script>  let el_down = document.getElementById("GFG_DOWN");  function Geeks() {  try {  let str = 'Hello, '  + 'Geeks'; // Error Here  el_down.innerHTML =  "'Invalid assignment left-hand side'" +  "error has not occurred";  } catch (e) {  el_down.innerHTML =  "'Invalid assignment left-hand side'" +  "error has occurred";  }  }   </script> </body> </html>