referenceerror invalid left hand side in assignment javascript

JS Tutorial
JS Exercise
JS Interview Questions
JS Operator
JS Projects
JS Examples
JS Free JS Course
JS A to Z Guide
JS Formatter

JavaScript ReferenceError – Invalid assignment left-hand side

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.

Error Type:

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

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

Output:

Improve your Coding Skills with Practice

What kind of Experience do you want to share?

Invalid left-hand side in assignment in JavaScript [Solved]

Last updated: Mar 2, 2024 Reading time · 2 min

# Invalid left-hand side in assignment in JavaScript [Solved]

The "Invalid left-hand side in assignment" error occurs when we have a syntax error in our JavaScript code.

The most common cause is using a single equal sign instead of double or triple equals in a conditional statement.

To resolve the issue, make sure to correct any syntax errors in your code.

invalid left hand side in assignment error

Here are some examples of how the error occurs.

# Use double or triple equals when comparing values

The most common cause of the error is using a single equal sign = instead of double or triple equals when comparing values.

The engine interprets the single equal sign as an assignment and not as a comparison operator.

We use a single equals sign when assigning a value to a variable.

However, we use double equals (==) or triple equals (===) when comparing values.

# Use bracket notation for object properties that contain hyphens

Another common cause of the error is trying to set an object property that contains a hyphen using dot notation.

use bracket notation for object properties containing hyphens

You should use bracket [] notation instead, e.g. obj['key'] = 'value' .

# Assigning the result of calling a function to a value

The error also occurs when trying to assign the result of a function invocation to a value as shown in the last example.

If you aren't sure where to start debugging, open the console in your browser or the terminal in your Node.js application and look at which line the error occurred.

The screenshot above shows that the error occurred in the index.js file on line 25 .

You can hover over the squiggly red line to get additional information on why the error was thrown.

Borislav Hadzhiev

Web Developer