JavaScript SyntaxError - Unexpected number

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.