//获取id
function getId(id) {
    return (typeof id == "object") ? id : document.getElementById(id);
}

//获取ClassName
function getElementsByClassName(name) {
    var tags = document.getElementsByTagName('*') || document.all;
    var els = [];
    for (var i = 0; i < tags.length; i++) {
        if (tags.className) {
            var cs = tags.className.split(' ');
            for (var j = 0; j < cs.length; j++) {
                if (name == cs[j]) {
                    els.push(tags);
                    break
                }
            }
        }
    }
    return els
}

//解决IE8之类不支持getElementsByClassName
if (!document.getElementsByClassName) {
    document.getElementsByClassName = function(className, element) {
        var children = (element || document).getElementsByTagName('*');
        var elements = new Array();
        for (var i = 0; i < children.length; i++) {
            var child = children[i];
            var classNames = child.className.split(' ');
            for (var j = 0; j < classNames.length; j++) {
                if (classNames[j] == className) {
                    elements.push(child);
                    break;
                }
            }
        }
        return elements;
    };
}

for(var i = 0; i < 10; i ++){

}

console.log(i); //10