处理来自无法解析的输入到JSON.parse（）的异常

Question

I came across this issue while creating a way to manage cookies in JS. My cookies can contain strings that are in JSON format:

var cookieContents = '{"type":"cookie","isLie":true}';

... or that are just plain strings:

var cookieContents = 'The cookie is a lie';

To parse the cookie, I would ideally do JSON.parse(cookieContents) . The problem with this is JSON.parse() cannot parse a plain string and throws a fatal error.

My question is what is the best/most widely accepted way to handle a situation like this?

I have tried using a try/catch statement:

var cookie1 = '{"type":"cookie","isLie":true}';
var cookie2 = 'The cookie is a lie';

function parseCookieString(str){
    var output;

    try{
        output = JSON.parse(str);
    } catch(e){
        output = str;
    }

    console.log(output);
}

parseCookieString(cookie1); // outputs object
parseCookieString(cookie2); // outputs string

http://jsfiddle.net/fmpeyton/7w60cesp/

This works perfectly fine, but feels dirty. Maybe because I usually do not handle JS fatal errors. Is it very common to handle fatal errors more gracefully in a scenario like this?

Answer 1

Doing a try catch makes sense but if JSON.parse throws an error because of something else than your output variable could end up containing something that you did not intend.

That's an interesting problem though. I would do something like this - basically checking for the presence of { and } in the string:

function parseCookieString(str){
    var output;

    if (!!str.match(/^{.+}$/)) {
      output = JSON.parse(str);
    } else {
      output = str;
    }

    console.log(output);
}

parseCookieString(cookie1); // outputs object
parseCookieString(cookie2); // outputs string