字符串Concat在范围JS中不起作用 [英] String Concat not working in scope JS

问题描述

在下面的代码中，我无法将变量 temp 连接到变量 newString .我进行了测试，发现这不是范围界定的问题，但是我仍然对此行为感到困惑.

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.

了解代码的目标

在下面，您将看到一个代码示例，该代码采用带有K(一个数字)和S(一个字符串)的对象.该功能旨在将字符在字母中的位置移位数字K，同时对于给定的String S，将其自身保持为大写或小写.

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
}

示例输入:

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

示例输出:

"Spwwz - Hzcwo"

再次，我对理解为什么concat无法优化代码本身更感兴趣.

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

推荐答案

您没有将值保存回 newString ( concat 不会对字符串值)，将其替换为

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

newString = newString.concat(temp);

和

newString = newString + word;//outside if

您也不能将值重新分配给 const ，因此请替换

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

const newString = ''

使用

var newString = ''

演示

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'
}));

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