计算字符串中每个字符出现次数

function charCntInString (argument) {
    var str = argument,result = [],beforeLen,afterLen;
    str = str.replace(/( |,)/ig, "");
    var strArr = str.split("");
    for (var i = 0; i < strArr.length; i++) {
        //str里的长度一直在变化。strArr里的字符可能在str里多次，但只有第一次匹配
        if(str.indexOf(strArr[i]) != -1){
            beforeLen = str.length;
            var reg = new RegExp(strArr[i], "ig");
            str2 = str.replace(reg,"");//字符串变短
            afterLen = str2.length;
            result.push(strArr[i]+":"+(beforeLen-afterLen));
            str = str2;
        }
    }
    return result.sort(sortNum);
}
function sortNum (p1,p2) {
    var n1 = p1.split(":")[1];
    var n2 = p2.split(":")[1];
    return n2-n1;//从大到小  从小到大n1-n2;
}


//var s = "This section of the site is dedicated to the JavaScript language itself, the parts that are not specific to Web pages or other host";
var s = "hello,world";
var ret = charCntInString(s);
console.log(ret);