Array.prototype.findLastIndex()

[teriyakigod2]

indexOf() - lastIndexOf()
findIndex() -  ????

Why do we have findIndex method, but no findLastIndex? It seems logical to follow[index|lastIndex]Of` pair, doesn't it? Reversing array to find the last element satisfies the condition seems too complicated to me.

Example:

function isPrime(element, index, array) {
  var start = 2;
  while (start <= Math.sqrt(element)) {
    if (element % start++ < 1) {
      return false;
    }
  }
  return element > 1;
}

console.log([4, 6, 8, 12].findIndex(isPrime)); // -1, not found
console.log([7, 4, 6, 7, 12].findIndexLast(isPrime)); // 3

Would be glad to implement, if it makes sense.

Thx for replies.

[WebReflection]

FWIW, indexOf => lastIndexOf so that findIndex => findLastIndex is the only name that makes sense to me.

However, reduce => reduceRight is also a thing so maybe findIndexRight would make sense too?

That leaves room for forEachRight, someRight, everyRight as well, so maybe it's a bit too much to ask :-)

[WebReflection]

FWIW, indexOf => lastIndexOf so that findIndex => findLastIndex is the only name that makes sense to me.

However, reduce => reduceRight is also a thing so maybe findIndexRight would make sense too?

That leaves room for forEachRight, someRight, everyRight as well, so maybe it's a bit too much to ask :-)

[ljharb]

Maybe somebody can speak to any motivation for not adding it.

However, please see https://github.com/tc39/ecma262/blob/master/CONTRIBUTING.md for how to best suggest new features for the language.

[ljharb]

Maybe somebody can speak to any motivation for not adding it.

However, please see https://github.com/tc39/ecma262/blob/master/CONTRIBUTING.md for how to best suggest new features for the language.

[teriyakigod2]

@ljharb Thx, my fault i didn't read it out before.

[teriyakigod2]

@ljharb Thx, my fault i didn't read it out before.