The Unexpected number error in JavaScript occurs when the JavaScript engine encounters a number in a place where it isn’t syntactically valid. This error is categorized as a SyntaxError, indicating that there’s a problem with the structure of your code.

Message

SyntaxError: Unexpected number

Error Type

SyntaxError

Cause of the Error

The “Unexpected number” error arises when a numeral is improperly positioned or used within your JavaScript code. This can happen due to:

• Misplaced Numbers: Numbers appearing in contexts where they are not allowed.
• Malformed Expressions: Errors in the way expressions are written, often due to missing operators or incorrect concatenation.
• String Concatenation Issues: Including numbers in strings without proper concatenation.

Correct Usage

To avoid this error, ensure that numbers are used correctly in expressions, variables, and other structures. Properly format expressions and strings to align with JavaScript’s syntax rules.

Example 1: Misplaced Number

In this example, a number is placed directly after a variable without an operator or space, causing the error:

let result = 10 20; // SyntaxError: Unexpected number

Output:

SyntaxError: Unexpected number

Correction: Ensure that numbers are properly separated by operators or spaces.

let result = 10 + 20; // Correct usage

Example 2: Incorrect String Concatenation

In the given below example a number is incorrectly included within a string without proper concatenation, causing the error.

let message = "The result is: " 42;
console.log(message);

Ouptut:

SyntaxError: Unexpected number

Correction: Use concatenation to properly include numbers in strings.

let message = "The result is :" + 42; // Correct usage

The SyntaxError: Unexpected number indicates a problem with the placement or use of numerals in your code. To resolve it, ensure that numbers are used in the correct context, and that all expressions and strings are properly formatted and concatenated.

FAQs-JavaScript SyntaxError – Unexpected number

What causes a SyntaxError: Unexpected number?

This error is caused by improper placement or usage of numbers in your code, such as missing operators between numbers, incorrect string concatenation, or malformed expressions.

How do I fix a SyntaxError: Unexpected number?

Ensure numbers are correctly placed within expressions, variables, or strings. Check for missing operators and correct concatenation of strings with numbers.

What is the difference between SyntaxError: Unexpected number and ReferenceError?

SyntaxError: Unexpected number indicates a problem with the structure of the code, such as incorrect number placement. ReferenceError occurs when a variable or function is referenced before it is declared or initialized.

Can SyntaxError: Unexpected number occur in JSON data?

Yes, if JSON data contains a syntax error, such as a misplaced number or incorrect format, parsing the JSON with JSON.parse() will throw a SyntaxError.

How does SyntaxError: Unexpected number affect debugging?

This error indicates a syntax issue in your code that must be resolved for the code to run correctly. Debugging involves checking the correct placement of numbers and ensuring proper syntax in expressions and strings.