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