Build string by generating random characters step by step

Extract magic numbers into constants

• For instance, what do 126 and 32 represent in the following line?

  return String.fromCharCode(Math.floor(Math.random() * (126 - 32 + 1)) + 32)
  

  It is much better to extract magic numbers into constants, i.e. to annotate them with a semantically meaningful name:

  const HIGHEST_ASCII_PRINTABLE_CHARACTER = 126;
  const LOWEST_ASCII_PRINTABLE_CHARACTER = 32;
  

  But even when you replace the numbers by their constant's name, it isn't immediately clear what you're doing with -32, +32, Math.random() and Math.floor() there. Even if you are accustomed to random number generation, a dedicated function call is more readable with less redundancy and in fact is easier to reason about:

  return String.fromCharCode(getRandomInt(LOWEST_ASCII_PRINTABLE_CHARACTER, HIGHEST_ASCII_PRINTABLE_CHARACTER));
  

  Especially, with your old code, I had to look up Math.random() on MDN to make really sure that is produces a uniform distribution. Now you can just add a docblock comment to getRandomInt indicating that property.

• await sleep(1000 / 16) also features magic numbers.

Miscellaneous remarks

• Using async-await for waiting after each loop iteration is a good use case and really makes the code cleaner!

• Extracting only a single property with the object destructuring syntax (const {length} = builtWord) seems a bit unidiomatic to me as opposed to const length = builtWord.length. Apart from that, you are using length only once anyway, so I would drop that variable all together.

• Try to avoid global variables and interdependencies.

  • For example, builtWord as well as targetWord are shared (and the former even modified!) by main and updateWord. I would suggest making updateWord accepting both as arguments and returning the possibly newly built word:

    function tryUpdateWord(currentBuiltWord, targetWord) {
        // This is a good moment to introduce a sanity check as well
        if (currentBuildWord.length >= targetWord.length) {
          throw new Error('<todo>');
        }
    
        const nextChar = getRandomChar()
        process.stdout.write('\r')
        process.stdout.write(currentBuiltWord)
        process.stdout.write(nextChar)
        if (targetWord[currentBuildWord.length] === nextChar) {
            return currentBuiltWord + nextChar
        }
        else {
            return currentBuiltWord;
        }
    }
    

  • Since the interdependencies have now been eliminiated, I would also move the part reading the process arguments into main():

    async function main() {
        const targetWord = process.args[2]
        let builtWord = ''
    
        const SLEEP_PER_ITERATION = 1000 / 16;
        while (true) {
            builtWord = tryUpdateWord(builtWord, targetWord)
            if (builtWord === targetWord) {
                break
            }
            await sleep(SLEEP_PER_ITERATION)
        }
    }