function checkme()
{
alert(this.value);
}
此时this代表 是当前聚焦的可视HTML元素(focus element).比如一个下拉框，输入框等等。
最严密的说法如下:
http://www.quirksmode.org/js/this.html
In JavaScript
this always refers to the “owner” of the function we're executing, or rather, to the object that a function is a method of. When we define our faithful function doSomething() in a page, its owner is the page, or rather, the window object (or global object) of JavaScript. An onclick property, though, is owned by the HTML element it belongs to.
