wordDeveloping.js

function wordDeveloping(input) {
    let index = 0;
    let string = input[index];
    index++;
    let newString = '';

    while (string !== 'End') {
        let [command, value] = string.split(' ');
        let indexOccurance = false;

        if (command === 'Add') {
            newString += value;
        } else if (command === 'Upgrade') {
            let wordArray = Array.from(newString);
            for (let char of wordArray) {
                if (char === value) {
                    let charIndex = wordArray.indexOf(char);
                    let code = newString.charCodeAt(charIndex);
                    code += 1;
                    value = String.fromCharCode(code);
                    wordArray.splice(charIndex, 1, value)
                }
            }
            newString = wordArray.join('');
        } else if (command === 'Print') {
            console.log(newString);
        } else if (command === 'Index') {
            let wordArray = Array.from(newString);
            let charIndexes = [];
            for (let i = 0; i < wordArray.length; i++) {
                if (wordArray[i] === value) {
                    indexOccurance = true;
                    charIndexes.push(i);
                }
            }

            if (indexOccurance) {
                console.log(charIndexes.join(' '));
            } else {
                console.log('None');
            }
        } else if (command === 'Remove') {
            newString = newString.split(value).filter(Boolean).join('');
        }

        string = input[index];
        index++;
    }
}

wordDeveloping(["Add University",
    "Print",
    "Upgrade n",
    "Print",
    "Index i",
    "Remove sity",
    "Print",
    "End"]);

console.log('---');

wordDeveloping(["Add HelloWorld",
    "Upgrade e",
    "Print",
    "Index b",
    "Remove rl",
    "Print",
    "End"]);