在 javascript 中检查字符串或输入中的最后一个字符是否彼此相似

Question

我正在尝试创建一个简单的加法计算器。截至目前，我已成功显示数字并将它们连接起来。但我不想要的是当我点击加号（添加）按钮两次或更多次时，它也会与另一个加号连接。有没有办法让我点击加号按钮两次。第二个符号将不再显示。就像它检测到先前的输入是加号一样。它永远不会相互连接。对不起，如果我的英语不清楚。

当我多次点击添加按钮时出现示例错误：( 111++++222 ) 而不是 111+222

这是我的代码伙计们：

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>


  <style>

    body {

      margin: 0px auto;
      width: 600px;
    }
  p {

    font-size: 23px;
    float: left;
    padding: 30px;
    border: solid #336336 2px;
    margin: 20px;
  }
  </style>
</head>
<body>
  
  <h1 id="result">aaww </h1>


  <p id="1" class="one">1</p>
  <p id="2" class="two">2</p>


  </br></br>

  <p id="add">+</p>


  </br></br>

  <p id="equals">=</p>
 <!--  <p class="cancel">cancel</p> <p class="cancel">cancel</p> -->

  <p class="clear-tasks"> CLEAR</p>

  <script>


    //PLACE HOLDER FOR THE RESULT
    let Result = document.getElementById("result");
    Result.innerText = "RESULT HERE";

    // CLEAR BUTTON
    let clear = document.querySelector('.clear-tasks'); 
    // EVENT LISTENER TO CLEAR THE BUTTON
    clear.addEventListener('click', function(){ 
      Result.textContent = '';
    });

    let addition = document.querySelector("#add");
    addition.addEventListener('click',runEventAdd);
    function runEventAdd(e){
      Result.textContent += ' + ';
    }

    

    //ONE BUTTON
    const numberOne = document.querySelector('.one');

    // EVENT LISTENER TO CONCATINATE 1
    numberOne.addEventListener('click', runEvent);

    function runEvent(e) {
      if (Result.textContent === 'RESULT HERE') {
        Result.textContent = 1;
      } else {Result.textContent += 1;
      }
    }

    
     //TWO BUTTON
    const numberTwo = document.querySelector('.two');
    // EVENT LISTENER TO CONCATINATE 2
    numberTwo.addEventListener('click', runEvent2);

    function runEvent2(e) {
      if (Result.textContent === 'RESULT HERE') {
        Result.textContent = 2;
      } else {Result.textContent += 2;
      }
    }


  </script>
</body>
</html>

Answer 1

使用if 语句检查是否已经有运算符。我在 Java 中用 GUI 而不是 JS 做了类似的东西，但我就是这么做的，而且效果很好。如果您执行 if 语句，您可以使用 if(str.indexOf(operator) == -1) { do the concatenation。

Answer 2

检查结果的最后一个值。如果是'+'，则不要再添加'+'

    
    //PLACE HOLDER FOR THE RESULT
    let Result = document.getElementById("result");
    Result.innerText = "RESULT HERE";

    // CLEAR BUTTON
    let clear = document.querySelector('.clear-tasks'); 
    // EVENT LISTENER TO CLEAR THE BUTTON
    clear.addEventListener('click', function(){ 
      Result.textContent = '';
    
    });

    let addition = document.querySelector("#add");
    addition.addEventListener('click',runEventAdd);
    function runEventAdd(e){

      if(Result.innerText.slice(-1) != '+')
      {
      Result.textContent += ' + ';
      }
      
    
    }

    

    //ONE BUTTON
    const numberOne = document.querySelector('.one');

    // EVENT LISTENER TO CONCATINATE 1
    numberOne.addEventListener('click', runEvent);

    function runEvent(e) {
      if (Result.textContent === 'RESULT HERE') {
        Result.textContent = 1;
      } else {Result.textContent += 1;
      }
    }

    
  //TWO BUTTON
 const numberTwo = document.querySelector('.two');
    // EVENT LISTENER TO CONCATINATE 2
    numberTwo.addEventListener('click', runEvent2);

    function runEvent2(e) {
      if (Result.textContent === 'RESULT HERE') {
        Result.textContent = 2;
      } else {Result.textContent += 2;
      }
    }

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>


  <style>

    body {

      margin: 0px auto;
      width: 600px;
    }
  p {

    font-size: 23px;
    float: left;
    padding: 30px;
    border: solid #336336 2px;
    margin: 20px;
  }
  </style>
</head>
<body>
  
  <h1 id="result">aaww </h1>


  <p id="1" class="one">1</p>
  <p id="2" class="two">2</p>


  </br></br>

  <p id="add">+</p>


  </br></br>

  <p id="equals">=</p>
 <!--  <p class="cancel">cancel</p> <p class="cancel">cancel</p> -->

  <p class="clear-tasks"> CLEAR</p>


</body>
</html>

Answer 3

只需使用endsWith检查当前字符串是否以+:

结尾

addition.addEventListener('click',runEventAdd);
function runEventAdd(e){
  if (!Result.textContent.endsWith(' + '))
      Result.textContent += ' + ';
}

在 javascript 中检查字符串或输入中的最后一个字符是否彼此相似

Check if the last characters in a string or inputs are similar to each other in javascript

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