Javascript - missing array

Question

I need to write a JS function that creates an object from a given string. String characters are object characters. Repeated characters should not be included twice. The 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 for duplicate characters with alreadyInArr. However, when I record my own alreadyInArr, it is 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 conclusion:

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

Can someone explain why it is alreadyInArrempty, and yet the function still works as expected?

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

Answer 1

else , , console.log() , , .

if, :

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

, .

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"));

Hide result

Answer 2

:

const string = "aabbcc", result = {};

for(const char of string)
  result[char] = 0;

Answer 3

else , , includes() true.

.

Answer 4

 if (!(alreadyInArr.includes(charsArr[i]))) {
      charsObj[charsArr[i]] = 0;
    } else {
      alreadyInArr.push(charsArr[i]);
    }

alreadyInArr.includes !. : NOT ( Inarr CharrsArr [i] ), :

, , .

, ,

Answer 5

You can distribute carcters and display objects with the desired properties.

function objFromStr(inStr) {
    return Object.assign(...Array.from(inStr, k => ({ [k]: 0 })));
}

console.log(objFromStr('aaaabbc'));

Run codeHide result

Answer 6

As others have already pointed out, you do not allow access to the array so that you constantly rewrite your object and assign 0.

You can cut the code as follows:

var arr = "aabbc", obj = {};

function objFromStr(inStr) {        
    arr.split("").forEach(function(x){
        obj[x] !== undefined ? obj[x]++ : obj[x] = 1;
    });     
    return obj;
}

console.log(objFromStr(arr));

This way you do not need to click or track anything in a separate array. It will check obj to see if a key exists. If he does, he will add 1 to it, and if not, he will consider it equal to 1.