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}

我知道这可能是一个老问题，但我有一个简单的解决方案为低水平的JavaScript初学者。

作为一个初学者，我只能理解这个问题的一些解决方案，所以我使用了两个嵌套的FOR循环来检查字符串中的每个字符，为每个发现等于该字符的字符增加一个计数变量。

我创建了一个新的空白对象，其中每个属性键是一个字符，值是每个字符在字符串中出现的次数(count)。

例子函数:

function countAllCharacters(str) {
  var obj = {};
  if(str.length!==0){
    for(i=0;i<str.length;i++){
      var count = 0;
      for(j=0;j<str.length;j++){
        if(str[i] === str[j]){
          count++;
        }
      }
      if(!obj.hasOwnProperty(str[i])){
        obj[str[i]] = count;
      }
    }
  }
  return obj;
}

我用ramda js的解决方案:

const testString = 'somestringtotest'

const countLetters = R.compose(
  R.map(R.length),
  R.groupBy(R.identity),
  R.split('')
)

countLetters(testString)

链接到REPL。

该函数以字符串str作为参数，并计算字符串中每个唯一字符的出现次数。结果是每个字符的键值对。

var charFoundMap = {};//object defined
    for (var i = 0; i < str.length; i++) {

       if(!charFoundMap[ str[i] ])  {
        charFoundMap[ str[i] ]=1;
       } 
       else
       charFoundMap[ str[i] ] +=1;
       //if object does not contain this 
    }
    return charFoundMap;

} 

Split与RegExp的性能

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");

这是我的解决方案。很多解决方案已经张贴在我之前。但我喜欢在这里分享我的观点。

const mainStr = 'str1,str2,str3,str4';

const commaAndStringCounter = (str) => {
  const commas = [...str].filter(letter => letter === ',').length;
  const numOfStr = str.split(',').length;

  return `Commas: ${commas}, String: ${numOfStr}`;
}

// Run the code
console.log(commaAndStringCounter(mainStr)); // Output: Commas: 3, String: 4

这是我的REPL