String Concat not working in scope JS

Question

Unable to make String Concat work

In the code below I am not able to concat the variable temp to the variable newString. I have tested and seen that this is not an issue of scoping but I am still puzzled by this behavior.

Understanding the objective of the code

Below you can see an example of the code which takes an object with K (a number) and S (a string). The function is meant to shift the character's position in the alphabet by the number K while keeping itself as Upper or Lowercase for a given String S.

function shiftCharByInt(args){
  const numb = args.K
  const word = args.S
  let newString = ''

  for(let i=0;i<word.length;i++){
      let character = word.charAt(i)
      if(/^[a-z]+$/.test(character)){
          let indexOfChar = character.charCodeAt(0)
          indexOfChar+=numb
          while(indexOfChar > 122) indexOfChar -= 26;
          let temp = String.fromCharCode(indexOfChar)
          newString.concat(temp)
          continue;
      }
      if(/^[A-Z]+$/.test(character)){
          let indexOfChar = character.charCodeAt(0)
          indexOfChar+=numb
          while(indexOfChar > 90) indexOfChar -= 26;
          let temp = String.fromCharCode(indexOfChar)
          newString.concat(temp)
          continue;
      }
      newString += word
  }
  return newString
}

Example Input:

{
  K: 11,
  S: 'Hello - World'
}

Example Output:

"Spwwz - Hzcwo"

Again, I am more interested in understanding why concat does not work optimising the code itself.

Could you provide example output as well?

Boris Lobanov
– Boris Lobanov

2018-02-12 10:36:51 +00:00
Commented Feb 12, 2018 at 10:36 — Boris Lobanov
– Boris Lobanov, Commented Feb 12, 2018 at 10:36

gurvinder372 · Accepted Answer · 2018-02-12 11:20:56Z

3

You are not saving the value back to newString (concat doesn't mutate the string value), replace it by

newString = newString.concat(temp);

and

newString = newString + word;//outside if

Also you can't re-assign a value to const, so replace

const newString = ''

with

var newString = ''

Demo

function test(args){
  const numb = args.K
  const word = args.S
  var newString = ''

  for(let i=0;i<word.length;i++){
    debugger
      let character = word.charAt(i)
      if(/^[a-z]+$/.test(character)){
          let indexOfChar = character.charCodeAt(0)
          indexOfChar+=numb
          while(indexOfChar > 122) indexOfChar -= 26;
          let temp = String.fromCharCode(indexOfChar)
          newString = newString.concat(temp)
          continue;
      }
      if(/^[A-Z]+$/.test(character)){
          let indexOfChar = character.charCodeAt(0)
          indexOfChar+=numb
          while(indexOfChar > 90) indexOfChar -= 26;
          let temp = String.fromCharCode(indexOfChar)
          newString = newString.concat(temp)
          continue;
      }
      newString = newString + character; 
  }
  return newString
}

console.log(test({
  K: 11,
  S: 'Hello - World'
}));

edited Feb 12, 2018 at 11:20

answered Feb 12, 2018 at 10:35

gurvinder372

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4 Comments

William Over a year ago

thanks, yes the last bit was meant to be newString = newString + character

gurvinder372 Over a year ago

@William What is the expected output?

William Over a year ago

Another small error, I put indexOfChar -= 25; instead of indexOfChar -= 26; for the input recommended we expected: ""Spwwz - Hzcwo""

gurvinder372 Over a year ago

@William Check the edited code, you need to keep newString = newString + character;

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