Unknown behaviour of Object.values() in Arrow Function

Question

I'm making a random password generator in Vannila JS , I'm facing a unknown problem in following code :

function generatePassword(lower, upper, number, symbol, length) {
  let generatedPassword = "";
  const typesCount = lower + upper + number + symbol;
  const typesArr = [{ lower }, { upper }, { number }, { symbol }].filter(
    (item) => Object.values(item)[0]
  );

  // Doesn't have a selected type
  if (typesCount === 0) {
    return "";
  }

  // create a loop
  for (let i = 0; i < length; i += typesCount) {
    typesArr.forEach((type) => {
      const funcName = Object.keys(type)[0];
      generatedPassword += randomFunc[funcName]();
    });
  }

  const finalPassword = generatedPassword.slice(0, length);

  return finalPassword;
}

In this block of code specifically the Object.values(item)[0] doesn't work if I enclose the statement in Curly Braces {} :

const typesArr = [{ lower }, { upper }, { number }, { symbol }].filter(
    (item) => Object.values(item)[0]
  );

I don't understand why this is happening , I tried searching docs but no avail , Thanks !

I checked the console but I doesn't seem to give error when I enclose it in curly braces , but the code doesn't work either... But If the curly braces are removed code works just fine — Yash Kadam
– Yash Kadam, Commented Apr 12, 2020 at 7:54
Do you mean it doesn't work if you write const typesArr = [{ lower }, { upper }, { number }, { symbol }].filter( (item) => { Object.values(item)[0] } ); — Shubham Khatri
– Shubham Khatri, Commented Apr 12, 2020 at 7:54
Exactly , It doesn't work this way & doesn't even show any errors — Yash Kadam
– Yash Kadam, Commented Apr 12, 2020 at 7:56
.filter( (item) => Object.values(item)[0] ); what are you trying so in this code. Did you mean to use .map() method, because filter is used to filter an array and then return that value not to return a specific value. — palaѕн
– palaѕн, Commented Apr 12, 2020 at 7:59

Shubham Khatri · Accepted Answer · 2020-04-12 07:58:31Z

1

In order for Filter function to correctly work, it needs to return. a truthy of falsy value.

When you write it like

const typesArr = [{ lower }, { upper }, { number }, { symbol }].filter(
    (item) => Object.values(item)[0]
  );

The result is implicitly return ie. Object.values(item)[0] is a returned value

However if you write it like

const typesArr = [{ lower }, { upper }, { number }, { symbol }].filter(
    (item) => { Object.values(item)[0] }
  );

You haven't returned any value from the filter function, you would need to add a return statement for it like

const typesArr = [{ lower }, { upper }, { number }, { symbol }].filter(
    (item) => { return Object.values(item)[0]; }
);

answered Apr 12, 2020 at 7:58

Shubham Khatri

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1 Comment

Dark Knight Over a year ago

if you can answer this stackoverflow.com/questions/61204297/… please

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