数字前加0

 //迭代方式实现function padding1(num, length) {for(var len = (num + "").length; len < length; len = num.length) {num = "0" + num;}return num;}//递归方式实现function padding2(num, length) {if((num + "").length >= length) {return num;}return padding2("0" + num, length)}//转为小数function padding3(num, length) {var decimal = num / Math.pow(10, length);//toFixed指定保留几位小数decimal = decimal.toFixed(length) + "";return decimal.substr(decimal.indexOf(".")+1);}//填充截取法function padding4(num, length) {//这里用slice和substr均可return (Array(length).join("0") + num).slice(-length);}//填充截取法function padding5(num, length) {var len = (num + "").length;var diff = length - len;if(diff > 0) {return Array(diff).join("0") + num;}return num;}

num：数字
length：数字最后的长度