js 常用函数收集（基础）

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;
    }
}