function isNum(obj){

  return !isNaN(parseFloat(obj)) && isFinite(obj);

}

function isEmptyObject(){

  var name;

  //遍历不是空对象返回

  for (name in obj) {

        return false;

   }

  return true;

}

function select(start, end) {

  var total = end - start +1;

  return Math.floor(Math.random() * total + start);

}

// 类型判断

function isType(type){

    return function(o){

        return Object.prototype.toString.call(o) === '[object ' + type + ']';

    }

}

var isString = isType(“String”);

var isObject = isType("Object");

var isArray = isType("Array");

isString("I'm Barret Lee.");

isArray([1,2,3])；

isObject({});

function $(objectId) {

if(document.getElementById && document.getElementById(objectId)) {

    return document.getElementById(objectId);// W3C DOM

    } else if (document.all && document.all(objectId)) {

        return document.all(objectId);// MSIE 4 DOM

    } else if (document.layers && document.layers[objectId]) {

        return document.layers[objectId];// NN 4 DOM.. note: this won't find nested layers

    } else {

        return false;

    }

}

function getStyle(obj, attr){

    if(obj.currentStyle){

        return obj.currentStyle[attr];

    }

    else{

        return getComputedStyle(obj,false)[attr];

    }

}