When I was writing line comments I had to solve the problem of parsing strings to JSON when the string wasn’t quite a properly formatted JSON string. Properly formatted JSON strings have double quotes around the keys and values.


But I didn’t want the user to have to type a bunch of double quotes. I wanted I wanted to let the user write a JSON object like this:

{key: value}


I started by using JSON.parse(). But JSON.parse() requires a properly formatted JSON string. That means you have to type the double quotes.

eval() - Never use eval!

Next I found the eval() method. eval() takes a string and runs it as JavaScript code. eval worked! It can take a string without double quotes and turn it into a JSON object. But you should never use eval!


eval() is a dangerous function, which executes the code it's passed with the privileges of the caller. If you run eval() with a string that could be affected by a malicious party, you may end up running malicious code on the user's machine with the permissions of your webpage / extension. More importantly, a third-party code can see the scope in which eval() was invoked, which can lead to possible attacks in ways to which the similar Function is not susceptible.

Write your own JSON parse

Then I tried writing my own JSON parse method that could handle the absence of the double quotes. Parsing objects from strings without given delimiters is a surprisingly complex problem. I got it partially working, but kept coming up with more edge cases that would be inconvenient for the users to deal with. So I looked for a library that had already solved the problem.

Import a library - JSON5 or other

I searched for relaxed JSON parser. After reading a couple of stack overflow answers, I found JSON5. It’s not the only relaxed JSON parser, but it was available on a CDN and it worked for my purposes.

Lesson Learned

Sometimes it’s worth it to reinvent the wheel as a learning exercise or to keep your code self contained. Other times it is a better choice to import a library because solving the problem yourself will take more time than it’s worth!