var a = "acvbasbb";
var b= {};
for (let i=0;i<a.length;i++){
    if((a.match(new RegExp(a[i], "g"))).length > 1){
        b[a[i]]=(a.match(new RegExp(a[i], "g"))).length;
    }
}
console.log(b);

In javascript you can use above code to get occurrence of a character in a string.

I know this might be an old question but I have a simple solution for low-level beginners in JavaScript.

As a beginner, I could only understand some of the solutions to this question so I used two nested FOR loops to check each character against every other character in the string, incrementing a count variable for each character found that equals that character.

I created a new blank object where each property key is a character and the value is how many times each character appeared in the string(count).

Example function:-

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;
}

The function takes string str as parameter and counts occurrence of each unique characters in the string. The result comes in key - value pair for each character.

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;

} 

My solution:

function countOcurrences(str, value){
   var regExp = new RegExp(value, "gi");
   return str.match(regExp) ? str.match(regExp).length : 0;  
}

And there is:

function character_count(string, char, ptr = 0, count = 0) {
    while (ptr = string.indexOf(char, ptr) + 1) {count ++}
    return count
}

Works with integers too!

我正在使用Node.js v.6.0.0，最快的是带有索引的索引（Lo Sauer的答案中的第三种方法）。

第二个是：

function count(s, c) {
  var n = 0;
  for (let x of s) {
    if (x == c)
      n++;
  }
  return n;
}

那么string.split（desiredCharecter）.length-1

例：

var str =“让生活变得更美好”; var len = str.split（“ h”）。length-1; 将为上述字符串中的字符“ h”提供计数2；

我正在做一个需要子字符串计数器的小项目。搜索错误的短语给我没有任何结果，但是在编写自己的实现之后，我偶然发现了这个问题。无论如何，这是我的方式，它可能比这里的大多数慢，但可能对某人有所帮助：

function count_letters() {
var counter = 0;

for (var i = 0; i < input.length; i++) {
    var index_of_sub = input.indexOf(input_letter, i);

    if (index_of_sub > -1) {
        counter++;
        i = index_of_sub;
    }
}

http://jsfiddle.net/5ZzHt/1/

如果您发现此实现失败或不遵循某些标准，请告诉我！:)

更新 您可能想要替代：

    for (var i = 0; i < input.length; i++) {

带有：

for (var i = 0, input_length = input.length; i < input_length; i++) {

有趣的阅​​读内容讨论了上述内容：http : //www.erichynds.com/blog/javascript-length-property-is-a-stored-value

我发现，搜索很大字符串（例如，长度为1 000 000个字符）中的字符的最佳方法是使用该replace()方法。

window.count_replace = function (str, schar) {
    return str.length - str.replace(RegExp(schar), '').length;
};

您可以看到另一个JSPerf套件来测试此方法以及其他在字符串中查找字符的方法。

这是一个类似的解决方案，但它使用 Array.prototype.reduce

function countCharacters(char, string) {
  return string.split('').reduce((acc, ch) => ch === char ? acc + 1: acc, 0)
}

如前所述，String.prototype.split工作速度比快得多String.prototype.replace。

将此功能添加到sting原型：

String.prototype.count=function(c) { 
  var result = 0, i = 0;
  for(i;i<this.length;i++)if(this[i]==c)result++;
  return result;
};

用法：

console.log("strings".count("s")); //2