JavaScript Program to Count the Occurrences of Each Character

This article will demonstrate different approaches for implementing a JavaScript program to count the occurrences of each character in a string. We will be given a string as input and we return the chars used with the number it occurred in that string.

Approaches to count the occurrences of each character

• Using JavaScript objects
• Using JavaScript map
• Using JavaScript array

Method 1: Using JavaScript Objects

In this method, we will create a JavaScript object that will store all the characters and their occurrences to accomplish the task.

Example: In this example, we will store chars and their occurrences in the result object using for loop for iteration.

Javascript

let str = 'GeeksforGeeks'

let result = {}
for(let i = 0;i< str.length;i++){
  let ch = str.charAt(i)
  if(!result[ch]){
    result[ch] =1;
  }
  else{
    result[ch]+=1
  }
}
console.log(
    "The occurrence of each letter in given string is:",result)

Output

The occurrence of each letter in given string is: { G: 2, e: 4, k: 2, s: 2, f: 1, o: 1, r: 1 }

Method 2: Using JavaScript Map

In this method, JavaScript map is used so that we can store the result in thje form of key-value pairs where key is the chars used and value will be the number of occurrences.

Example: In this example, we will iterate the given string and store result in the form of key-value pairs.

Javascript

let str = 'GeeksforGeeks'

let result = new Map()
for(let i = 0;i< str.length;i++){
  let ch = str.charAt(i)
  if (!result.get(ch)) result.set(ch, 1);
    else {
        result.set(ch, result.get(ch) + 1);
    }
}
console.log(result)
// console.log(
    // "The occurrence of each letter in given
    // string is:",result)

Output

Map(7) {
  'G' => 2,
  'e' => 4,
  'k' => 2,
  's' => 2,
  'f' => 1,
  'o' => 1,
  'r' => 1
}

Method 3: Using JavaScript Array

In this method, we will use JavaScript Array to get the chars and occurrences by converting the string in array and then apply JavaScript array methods.

Example: In this example, we will use array reduce to return an array that contains the chars and their occurrences.

Javascript

let str = "GeeksforGeeks";

let strArray = str.split("");

// console.log(strArray)
let result = strArray.reduce((chars, ch) => {
    if (!chars[ch]) {
        chars[ch] = 1;
    } else {
        chars[ch] += 1;
    }
    // console.log(ch);
    return chars;
}, []);

// console.log(result)
console.log(
    "The occurrence of each letter in given string is:", result)

Output

The occurrence of each letter in given string is: [
  G: 2, e: 4,
  k: 2, s: 2,
  f: 1, o: 1,
  r: 1
]