s = 'dir/dir/dir/dir/'
for(i=l=0;i<s.length;i++)
if(s[i] == '/')
l++

下面使用正则表达式测试长度。Testex确保不存在16个或更多的连续非逗号字符。如果它通过了测试，那么它将继续拆分字符串。计算逗号的数量就像计算符号减1一样简单。

var mainStr = "str1,str2,str3,str4";
var testregex = /([^,]{16,})/g;
if (testregex.test(mainStr)) {
  alert("values must be separated by commas and each may not exceed 15 characters");
} else {
  var strs = mainStr.split(',');
  alert("mainStr contains " + strs.length + " substrings separated by commas.");
  alert("mainStr contains " + (strs.length-1) + " commas.");
}

最简单的办法是…

的例子,

str = 'mississippi';

function find_occurences(str, char_to_count){
    return str.split(char_to_count).length - 1;
}

find_occurences(str, 'i') //outputs 4

let str = "aabgrhaab"
let charMap = {}

for(let char of text) {
   if(charMap.hasOwnProperty(char)){
      charMap[char]++
   } else {
     charMap[char] = 1
   }
}

console.log (charMap);//{a: 4, b: 2, g: 1, r: 1, h: 1}

var i = 0; var split_start = new Date().getTime(); while (i < 30000) { "1234,453,123,324".split(",").length -1; i++; } var split_end = new Date().getTime(); var split_time = split_end - split_start; i= 0; var reg_start = new Date().getTime(); while (i < 30000) { ("1234,453,123,324".match(/,/g) || []).length; i++; } var reg_end = new Date().getTime(); var reg_time = reg_end - reg_start; alert ('Split Execution time: ' + split_time + "\n" + 'RegExp Execution time: ' + reg_time + "\n");

下面是最简单的逻辑，很容易理解

  //Demo string with repeat char 
  let str = "Coffee"
  //Splitted the str into an char array for looping
  let strArr = str.split("")
  //This below is the final object which holds the result
  let obj = {};
  //This loop will count char (You can also use traditional one for loop)
  strArr.forEach((value,index)=>{
      //If the char exists in the object it will simple increase its value
      if(obj[value] != undefined)
      {
          obj[value] = parseInt(obj[value]) + 1;
      }//else it will add the new one with initializing 1
      else{
          obj[value] =1;
      }      
  });

  console.log("Char with Count:",JSON.stringify(obj)); //Char with Count:{"C":1,"o":1,"f":2,"e":2}