document.ready will execute after all HTML of the page is loaded.

window.load will wait for all elements are loaded, include image, iframe. window.load can be used in body onload.

$(document).ready will trigger before $(window).load. Use window.load when you want retrieve attribute of image, iframe on page start.

The 'string' keyword is equivalent of 'System.String' so you don't need to using namespace System like following code.

//using System;
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string s1 = string.Empty;
            System.String s2 = System.String.Empty;
            String s3 = String.Empty; // compile error namespace could not be found
        }
    }
}