Can anyone explain how this "e.target.dataset.num" works in this code? Thanks in advance

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<!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>Recording</title>
 <link rel="stylesheet" href="main.css">
</head>

<body>
 <section class="calculator">
  <form>
   <input type="text" name="" id="" class="screen">
  </form>
  <div class="buttons">
   <!-- yellow -->
   <button type="button" class="btn btn-yellow" data-num="*">*</button>
   <button type="button" class="btn btn-yellow" data-num="/">/</button>
   <button type="button" class="btn btn-yellow" data-num="-">-</button>
   <button type="button" class="btn btn-yellow" data-num="+">+</button>
   <!-- grey buttons -->
   <button type="button" class="btn btn-grey" data-num=".">.</button>
   <button type="button" class="btn btn-grey" data-num="9">9</button>
   <button type="button" class="btn btn-grey" data-num="8">8</button>
   <button type="button" class="btn btn-grey" data-num="7">7</button>
   <button type="button" class="btn btn-grey" data-num="6">6</button>
   <button type="button" class="btn btn-grey" data-num="5">5</button>
   <button type="button" class="btn btn-grey" data-num="4">4</button>
   <button type="button" class="btn btn-grey" data-num="3">3</button>
   <button type="button" class="btn btn-grey" data-num="2">2</button>
   <button type="button" class="btn btn-grey" data-num="1">1</button>
   <button type="button" class="btn btn-grey" data-num="0">0</button>
   <button type="button" class="btn-equal btn-grey">=</button>
   <button type="button" class="btn-clear btn-grey">C</button>
  </div>
 </section>
 <script>
      //Wrap code in an IIFE
(function(){
  
  let screen = document.querySelector('.screen');
  let buttons = document.querySelectorAll('.btn');
  let clear = document.querySelector('.btn-clear');
  let equal = document.querySelector('.btn-equal');
  
  //retrieve data from numbers that are clicked
  buttons.forEach(function(button){
    button.addEventListener('click', function(e){
      let value = e.target.dataset.num;
      screen.value += value;
    })
  });
  
  equal.addEventListener('click', function(e){
    if(screen.value === ''){
      screen.value = 'Please Enter a Value';
    } else {
      let answer = eval(screen.value);
      screen.value = answer;
    }
  })
  
  clear.addEventListener('click', function(e){
    screen.value = '';
  })
 
})(); //end IIFE
</script>
</body>

</html>

What I have tried:

I tried googling this but could not get exact meaning of this "e.target.dataset.num" line..

Posted 29-May-21 14:38pm

Vaibhav Chowdhary

Updated 1-Jun-21 6:07am

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Richard Deeming · Accepted Answer · 2021-06-01T06:07:00

e.target is the element which was clicked:
Event.target - Web APIs | MDN[^]

.dataset returns the set of data-* attributes on that element:
HTMLOrForeignElement.dataset - Web APIs | MDN[^]
Using data attributes - Learn web development | MDN[^]

And finally, .num returns the value of the data-num attribute.

Quote:
Attributes can be set and read by the camelCase name/key as an object property of the dataset: element.dataset.keyname