var a = 元素本身的寬度;
width() = a;
innerWidth() = a+padding;
outerWidth() = a+padding+border;
outerWidth(true) = a+padding+border+margin;
var a = 元素本身的寬度;
width() = a;
innerWidth() = a+padding;
outerWidth() = a+padding+border;
outerWidth(true) = a+padding+border+margin;