Counting frequency of characters in a string using JavaScript

I need to write some kind of loop that can count the frequency of each letter in a string.

For example: "aabsssd"

output: a:2, b:1, s:3, d:1

Also want to map same character as property name in object. Any good idea how to do this?

I am not sure how to do it.

This is where I am so far:

var arr = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"];

function counter(x) {
  var count = 0,
    temp = [];
  x = x.split('');
  console.log(x);
  for (var i = 0, len = x.length; i < len; i++) {
    if (x[i] == "a") {
      count++;
    }
  }
  return count;
}
var a = "aabbddd";
console.log(counter(a));

Here you go:

function getFrequency(string) {
    var freq = {};
    for (var i=0; i<string.length;i++) {
        var character = string.charAt(i);
        if (freq[character]) {
           freq[character]++;
        } else {
           freq[character] = 1;
        }
    }

    return freq;
};

some ES6 syntax with reduce:

let counter = str => {
  return str.split('').reduce((total, letter) => {
    total[letter] ? total[letter]++ : total[letter] = 1;
    return total;
  }, {});
};

counter("aabsssd"); // => { a: 2, b: 1, s: 3, d: 1 }

Another solution:

function count (string) {  
  var count = {};
  string.split('').forEach(function(s) {
     count[s] ? count[s]++ : count[s] = 1;
  });
  return count;
}