Question

jQuery.parseJSON and JSON.parse are two functions that perform the same task. If the jQuery library is already loaded, would using jQuery.parseJSON be better than using JSON.parse, in terms of performance?

If yes, why? If no, why not?

Answer 1

Here is an extract from jQuery 1.9.1:

parseJSON: function( data ) {
    // 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 );
},

As you can see, jQuery will use the native JSON.parse method if it is available, and otherwise it will try to evaluate the data with new Function, which is kind of like eval.

So yes, you should definitely use jQuery.parseJSON.