JSON-parse-Error.html - JSON.parse() Errors

Q

How to catch errors when calling the JSON.parse() function in JavaScript?

✍: FYIcenter.com

A

If you want to catch errors when calling the JSON.parse() function in JavaScript, you can follow this tutorial:

1. Use the "try {...} catch {...}" block to catch the error object throw from the JSON.parse() function, as shown below:

   try {
      var val = JSON.parse(...);
    ...
   } catch (err) {
      ...
   }

2. Print out the "message" string from the error object back to the user or the log file. The message string gives more details about the error, as shown below:

   try {
      ...
   } catch (err) {
      document.write("   err.message = "+err.message+"\n");
      ...
   }

3. Enter the following example JavaScript code in a file, JSON-parse-Error.html:

<!-- JSON-parse-Error.html
     Copyright (c) FYIcenter.com
-->
<html>
<body>
<script type="text/javascript">
   try {
      var val1 = JSON.parse('2020');             // Valid
      var val2 = JSON.parse('"foo"');            // Valid
      var val3 = JSON.parse('[1, 5, "false",]'); // Invalid
   
      document.write("<p>Value from JSON.parse():</p>");
      document.write("<pre>");
      document.write("   val1.toString() = "+val1.toString()+"\n");
      document.write("   val2.toString() = "+val2.toString()+"\n");
      document.write("   val3.toString() = "+val3.toString()+"\n");
      document.write("</pre>");
   } catch (err) {
      document.write("<p>Error from JSON.parse():</p>");
      document.write("<pre>");
      document.write("   err.message = "+err.message+"\n");
      document.write("</pre>");
   }
</script>
</body>
</html>

4. Save the above code in a file and open it in a Web browser. You see the following output:

Error from JSON.parse():
   err.message = Unexpected token ] in JSON at position 15

⇒ Call JSON.parse() with Reviver Function

⇐ JSON-parse.html - JSON.parse() Example Code

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