Learning jQuery

JSON.parse() and jQuery.parseJSON(), both are used to parse a JSON string and returns resulting JavaScript value or object described by the string. jQuery.parseJSON() is available only when jQuery library is used where JSON.parse() is JavaScript's standard built-in JSON object method. So the question is if jQuery library is used, then which one should be used or both gives same performance and result?

Well, the answer is that both are equal. As you know, jQuery's library is written on top of JavaScript. So  jQuery.parseJSON() makes use of JSON.parse() internally. Here is the code of jQuery.parseJSON() method from jQuery 1.9.1 library. As you can see, it first checks if JSON.parse is supported or not. If supported, then it makes use of JSON.parse only. Otherwise, it tries to evaluate string data with new Function.

// Attempt to parse using the native JSON parser first
if (window.JSON && window.JSON.parse) {
    return window.JSON.parse(data);
}

if (data === null) {
    return data;
}

if (typeof data === "string") {
    // Make sure leading/trailing whitespace is removed (IE can't handle it)
    data = jQuery.trim(data);
    if (data) {
        // Make sure the incoming data is actual JSON
        // Logic borrowed from http://json.org/json2.js
        if (rvalidchars.test(data.replace(rvalidescape, "@")
                .replace(rvalidtokens, "]")
                .replace(rvalidbraces, ""))) {

            return (new Function("return " + data))();
        }
    }
}
jQuery.error("Invalid JSON: " + data);
}

This was done as JSON.parse is natively available on some browsers, and jQuery is browser independent. So if JSON.parse is not available, then it falls back to jQuery implementation.

JSON.parse was not supported in old browsers like IE 7 and Safari 3, but over the period of time, browsers have also evolved. And now most of the browsers support JSON.parse. Therefore, the implementation of jQuery.parseJSON() is also changed after jQuery 2.0 release. Here is the code of new implementation from jQuery 2.2.4 library:

// Support: Android 2.3
// Workaround failure to string-cast null input
jQuery.parseJSON = function(data) {
    return JSON.parse(data + "");
};

And the big news is that with jQuery 3.0, jQuery.parseJSON is deprecated. So now to parse JSON objects, use the native JSON.parse method instead.