How to get the number of occurrences of each letter in specified string in JavaScript ?

In this article, we are given a string, our task is to find the occurrence of a character in the string with the help of a user-defined function. 

Example:
Input : "hello"
Output : h occur 1 times
         e occur 1 times
         l occur 2 times
         o occur 1 times
Explanation : here "hello" have 1 h, so it have 1 value.
               as same e have 1, l have 2 , o have 1.
Example 2:
Input : "did"
Output: d occur 2 times 
        i occur 1 times

Approach 1: In this approach, we use a map data structure to store the number of times characters occur.

• First, we initialize the map with a key for each character of the string, and the value for each is 0.
• We iterate over the string and increment the value of the character.
• Finally, print key-values of the map.

Example: This example shows the use of the above-explained approach.

Javascript

<script>
    //function to print occurrence of character
    function printans( ans )
    {
      for( let [ key ,value] of ans)
      {
        // if()
        console.log(`${key}  occurs  ${value} times` );

      }

    }

    // function count occurrence of character
    function count( str , outp_map )
    {
      for( let i = 0 ;i < str.length ;i++)
      {

        let k = outp_map.get(str[i]);
        outp_map.set(str[i], k+1) ;


      }
      //calling  print function
      printans(outp_map);
    }

    //function create map to count character
    function count_occurs( test , callback )
    {
      //checking string is valid or not
      if( test.length === 0 )
      {
        console.log(" empty string ");
        return ;
      }
      else
      {
        // map for storing count values
        let ans = new Map();
        for( let i = 0 ;i < test.length;i++)
        {
          ans.set(test[i], 0);
        }

        callback( test ,ans);

      }

    }

    // test string
    let test =  "helloworld";
    count_occurs( test ,count);
</script>

Output:

h  occurs  1 times
e  occurs  1 times
l  occurs  3 times
o  occurs  2 times
w  occurs  1 times
r  occurs  1 times
d  occurs  1 times

Approach 2: In this approach, we use nested for loop to iterate over the string and count for each character in the string. 

• First, initialize count with value 0 for the ith value of the string.
• Now we iterate over the string if ith value matches with the character, increasing the count value by 1.
• Finally, print the value of the count.

Example: This example shows the use of the above-explained approach.

Javascript

<script>
    // function that count character occurrences in string
    function count_occur( str )
    {
      // checking string is valid or not
      if( str.length == 0 )
      {
        console.log("Invalid string")
        return;
      }
      //cor loop to iterate over string
      for( let i = 0 ;i < str.length ;i++)
      {
        //variable counting occurrence
        let count = 0;
        for( let j = 0 ;j < str.length ;j++)
        {
          if( str[i] == str[j] && i > j  )
          {
           break;
          }
          if( str[i] == str[j]  )
          {
            count++;
          }
        }
        if( count > 0)
        console.log(`${str[i]} occurs ${count} times`);

      }

    }

    // test string
    let test_str = "gfghello";
    count_occur( test_str);
</script>

Output:

g occurs 2 times
f occurs 1 times
h occurs 1 times
e occurs 1 times
l occurs 2 times
o occurs 1 times