<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Hold Shift to Check Multiple Checkboxes</title>
</head>
<body>
  <div class="inbox">
    <div class="item">
      <input type="checkbox">
      <p>This is an inbox layout.</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Check one item</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Hold down your Shift key</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Check a lower item</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Everything in between should also be set to checked</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Try to do it without any libraries</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Just regular JavaScript</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Whee..</p>
    </div>
    <div class="item">
      <input type="checkbox">
      <p>Checkity check!</p>
    </div>
  </div>

<script>
</script>
</body>
</html>
  html {
      font-family: sans-serif;
      background: #ffc600;
    }
    .inbox {
      max-width: 400px;
      margin: 50px auto;
      background: white;
      border-radius: 5px;
      box-shadow: 10px 10px 0 rgba(0,0,0,0.1);
    }
    .item {
      display: flex;
      align-items: center;
      border-bottom: 1px solid #F1F1F1;
    }
    .item:last-child {
      border-bottom: 0;
    }
    input:checked + p {
      background: #F9F9F9;
      text-decoration: line-through;
    }
    input[type="checkbox"] {
      margin: 20px;
    }
    p {
      margin: 0;
      padding: 20px;
      transition: background 0.2s;
      flex: 1;
      font-family:'helvetica neue';
      font-size: 20px;
      font-weight: 200;
      border-left: 1px solid #D1E2FF;
    }
const checkboxes = document.querySelectorAll('input[type="checkbox"]')
//step 1: keep track of last checked box
//step 2: is shiftkey down?
    //if yes, check everyhing in btw
      //loop through all boxes again and check all in between
    //if no, just check current box

let lastChecked; //keep track of last checked box

function handleCheck(e){
  let inBetween = false; 
  if (e.shiftKey === true){
    checkboxes.forEach(item => {
       //keep track of in between boxes by toggling inBetween to be true for all boxes in between, and then toggle it back to false after. If you dont understand, go through line by line what happen to each box when click and shift.
       if (item === this || item === lastChecked){
         inBetween = !inBetween;
       }
       //check every box in between
       if (inBetween){
         item.checked = true;
       }
    })
  }
  
  lastChecked = this //keep track of last checked box
}

checkboxes.forEach(item => item.addEventListener('click', handleCheck));

External CSS

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External JavaScript

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