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json parse is insane

29 Oct 2014

every project i’ve been in so far had the same stupid bug with JSON.parse. at the beginning someone got a string instead of an object and they used JSON.parse to convert it to an object.
then after a while, someone fixed it upstream, and now JSON.parse is getting an object and fails with a very cryptic error message.

i always make sure my code is safe and i write it as such:

item =;
if ( typeof(item) === 'string' ) {   
   item = JSON.parse(item);  

however, each time i write this piece of code, it seems to me like it is a bug in javascript.

seems to me like 1 of 2 things should happen:

i think the latter is better and more aligned with the rest of JavaScript behavior. but what happens now is simply insane - JavaScript implicitly converts the object toString and tries to parse that.
which is insane because nowhere in the world of JavaScript is toString meant to return a JSON.
this is why you have JSON.stringify to begin with.
so if anything at all JSON.parse should use JSON.stringify instead of toString

another reason why this is insane is that toString returns [object Object] which ironically enough starts like an array (which is a valid input for JSON.parse) and so the error developers get is invalid token o.
and last reason for insanity is that this has been the situation for quite a while now.

i tried to see what other libraries are doing with this insanity : turns out that JQuery doesn’t try to fix this issue. $.JSONparse is just as insane.
lodash does not offer anything in this matter.
i know that angular behaves nicely - like i expected - but for projects that don’t use angular, it would be an overkill to use angular just for this.
other than that, I could not find any references to this problem anywhere.
this problem seems to me a lot like the console.log problem - that it does not exist in some browsers - and should have a similar fix.

my current recommendation to fix this issue by replacing JSON.parse method with something like

JSON.parseString = JSON.parse  
JSON.parse = function ( o ) {  
    if ( typeof(o)  === 'string' ){   
       return JSON.parseString.apply(arguments);  
    } else {   
        return o;   

but i keep getting strong objections on such a solution as it is intrusive. what do you think? leave comments below.

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