Chi Chan Chi Chan - 6 months ago 37
JSON Question

How to check if a string is a valid JSON string in JavaScript without using Try/Catch

Something like:

var jsonString = '{ "Id": 1, "Name": "Coke" }';

//should be true
IsJsonString(jsonString);

//should be false
IsJsonString("foo");
IsJsonString("<div>foo</div>")


The solution should not contain try/catch. Some of us turn on "break on all errors" and they don't like the debugger breaking on those invalid JSON strings.

Mic Mic
Answer

A comment first. The question was about not using try/catch.
If you do not mind to use it, read the answer below. Here we just check a JSON string using a regexp, and it will work in most cases, not all cases.

Have a look around the line 450 in https://github.com/douglascrockford/JSON-js/blob/master/json2.js

There is a regexp that check for a valid JSON, something like:

if (/^[\],:{}\s]*$/.test(text.replace(/\\["\\\/bfnrtu]/g, '@').
replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']').
replace(/(?:^|:|,)(?:\s*\[)+/g, ''))) {

  //the json is ok

}else{

  //the json is not ok

}