原生JS获取CSS的实现

function getStyle(id,styleName){
    var obj = document.getElementById(id);
    var style = null;
    if (window.getComputedStyle) {
        style = window.getComputedStyle(obj, null);    // 非IE
    } else { 
        style = obj.currentStyle;  // IE
    }
    return style[styleName];
}