javascript - missing array

Question

I need to write a JS function that creates an object from a given string. String characters are object keys. Repeated characters should not be included twice. Values of all keys are zero.

Example: input objFromStr("aaabc") should return {a: 0, b: 0, c: 0}

Here is my solution:

function objFromStr(inStr) {
  let charsArr = inStr.split("");

  let charsObj = {};
  var alreadyInArr = [];

  for (var i = 0; i < charsArr.length; i++) {
    if (!(alreadyInArr.includes(charsArr[i]))) {
      charsObj[charsArr[i]] = 0;
    } else {
      alreadyInArr.push(charsArr[i]);
    }
  }

  return charsObj;
}

This solution works as expected, but I don't understand why. I check chars duplication using alreadyInArr. However when I log my alreadyInArr, it's empty.

So after running this code:

function objFromStr(inStr) {
  let charsArr = inStr.split("");

  console.log("charsArr is:", charsArr);

  let charsObj = {};
  var alreadyInArr = [];

  for (var i = 0; i < charsArr.length; i++) {
    if (!(alreadyInArr.includes(charsArr[i]))) {
      charsObj[charsArr[i]] = 0;
    } else {
      alreadyInArr.push(charsArr[i]);
    }
  }

  console.log("alreadyInArr is:", alreadyInArr);

  return charsObj;
}

console.log(objFromStr("aaabc"));

My output is:

charsArr is: [ 'a', 'a', 'a', 'b', 'c' ]
alreadyInArr is: []
{ a: 0, b: 0, c: 0 }

Can someone explain, why alreadyInArr is empty and yet function still works as expected?

Here's a pen: https://codepen.io/t411tocreate/pen/bYReRj?editors=0012

Answer 1

Your else clause isn't reachable at all since you didn't pushed the element in the right place, you could add a console.log() inside the loop to see that the array still empty through all the iterations.

Instead, the element should be pushed in the if condition like :

for (var i = 0; i < charsArr.length; i++) {
    if (!alreadyInArr.includes(charsArr[i])) {
        charsObj[charsArr[i]] = 0;
        alreadyInArr.push(charsArr[i]);
    }
}

Hope this helps.

function objFromStr(inStr) {
  let charsArr = inStr.split("");

  console.log("charsArr is:", charsArr);

  let charsObj = {};
  var alreadyInArr = [];

  for (var i = 0; i < charsArr.length; i++) {
    if (!alreadyInArr.includes(charsArr[i])) {
      charsObj[charsArr[i]] = 0;
      alreadyInArr.push(charsArr[i]);
    }
  }

  console.log("alreadyInArr is:", alreadyInArr);

  return charsObj;
}

console.log(objFromStr("aaabc"));