js实现数字每三位加逗号的方法

function formatNum(str){var newStr = "";var count = 0;if(str.indexOf(".")==-1){   for(var i=str.length-1;i>=0;i--){ if(count % 3 == 0 && count != 0){   newStr = str.charAt(i) + "," + newStr; }else{   newStr = str.charAt(i) + newStr; } count++;   }   str = newStr + ".00"; //自动补小数点后两位   console.log(str)}else{   for(var i = str.indexOf(".")-1;i>=0;i--){ if(count % 3 == 0 && count != 0){   newStr = str.charAt(i) + "," + newStr; }else{   newStr = str.charAt(i) + newStr; //逐个字符相接起来 } count++;   }   str = newStr + (str + "00").substr((str + "00").indexOf("."),3);   console.log(str) }}formatNum('13213.24'); //输出13,213.34formatNum('132134.2');  //输出132,134.20formatNum('132134');  //输出132,134.00formatNum('132134.236');  //输出132,134.23