Unexpected character ('F' (code 70)): expected a valid value (number, String, array, object, 'true', 'false' or 'null') What does it mean?

ONLINECAST

2 min read

·

07-10-2024

3

0

Share

"Unexpected character ('F' (code 70)): expected a valid value..." - Decoding the JSON Error

Have you encountered the cryptic error message "Unexpected character ('F' (code 70)): expected a valid value..." while working with JSON data? This error often pops up when you're trying to parse a JSON string into a JavaScript object, and it signals a fundamental issue with the structure of your JSON data.

Let's break down what's going on and provide some solutions:

Understanding the Error:

JSON (JavaScript Object Notation) is a standard format for exchanging data. It's designed to be human-readable and easily processed by machines. The error message points to a specific character ('F') within your JSON string that the parser doesn't recognize as valid.

The Root of the Problem:

This error usually arises when you have one of these problems in your JSON:

• Invalid Data Type: JSON values can only be strings, numbers, booleans (true or false), null, objects, or arrays. The presence of 'F' might indicate an attempt to use a string where a number or boolean is expected.
• Incorrect Syntax: JSON follows strict syntax rules. A misplaced comma, missing quote marks, or unexpected characters can cause parsing errors.

Code Example and Explanation:

const jsonString = `{ "name": "John", "age": "F" }`; 

try {
  const jsonData = JSON.parse(jsonString);
  console.log(jsonData); // Output: Error!
} catch (error) {
  console.error(error); // Output: SyntaxError: Unexpected character ('F' (code 70)): expected a valid value (number, String, array, object, 'true', 'false' or 'null')
}

In this example, the age property is assigned the value 'F', which is not a valid JSON data type. The parser expects a number or a string enclosed in quotes.

Solutions and Best Practices:

1. Inspect Your JSON: Carefully review your JSON string for any syntax errors. Use a JSON validator online to help you pinpoint issues.
2. Correct Data Types: Make sure you're using the correct JSON data types for each value. If you intend to store a number, use a number instead of a string.
3. Validate Before Parsing: Before parsing, you can use a validation library like json-schema to verify the structure and data types in your JSON.
4. Use a JSON Library: Libraries like JSON.parse and JSON.stringify are essential for handling JSON in JavaScript. Use them effectively to avoid manual errors.

Additional Tips:

• Debugging Tools: Use browser developer tools or a debugger to inspect the JSON string and identify the offending character.
• JSON Formatter: Online JSON formatters can help you visually identify syntax errors and improve readability.

Remember: JSON follows a strict format. Understanding its rules and using the right tools will save you from countless headaches and help you efficiently work with JSON data.