Number of non-unique characters in a string in JavaScript

We are required to write a JavaScript function that takes in a string and returns the count of redundant characters in the string.

For example: If the string is −

const str = 'abcde'

Then the output should be 0.

If the string is −

const str = 'aaacbfsc';

Then the output should be 3.

Example

The code for this will be −

const str = 'aaacbfsc';
const countRedundant = str => {
   let count = 0;
   for(let i = 0; i < str.length; i++){
      if(i === str.lastIndexOf(str[i])){
         continue;
      };
      count++;
   };
   return count;
};
console.log(countRedundant(str));

Output

The output in the console will be −

3