How to change getElementbyId to getElementsbyClassName

Question

I'm trying to change the value of colspan using the below code but its only working for January. It should work for both January and February. By clicking the button the value of the colspan attribute, from 2 to 1, of td with id "myTd".

<!DOCTYPE html>
<html>
<head>
<style>
table, th, td {
  border: 1px solid black;
}
</style>
</head>
<body>

<p>Click the button to change the value of the colspan attribute, from 2 to 1, of td with id "myTd".</p>

<table>
  <tr>
    <th>Month</th>
    <th>Savings</th>
  </tr>
  <tr>
    <td id="myTd" colspan="2">January</td>
    <td>$100</td>
  </tr>
  <tr>
    <td id="myTd" colspan="2">February</td>
    <td>$100</td>
  </tr>
</table>
<br> 

<button onclick="myFunction()">Try it</button>

<script>
function myFunction() {
  document.getElementById("myTd").colSpan = "1";
}
</script>

</body>
</html>

`id="myTd"` IDs *must* be unique. As such, DOM methods such as getElementById or selectors such as `#myId` will only find the first, as they expect there to be only one. — freedomn-m, Sep 06 '22 at 13:41

score 1 · Accepted Answer · answered Sep 06 '22 at 13:40

The cause of your issue is because you've repeated the same id on multiple elements, which is invalid. id must be unique within the DOM. Change these to common class attributes.

From there you can use querySelectorAll() and loop through the resulting collection to update their colspan:

document.querySelector('button').addEventListener('click', e => {
  document.querySelectorAll(".myTd").forEach(el => el.colSpan = "1");
});

table,
th,
td {
  border: 1px solid black;
}

<p>Click the button to change the value of the colspan attribute, from 2 to 1, of td with id "myTd".</p>

<table>
  <tr>
    <th>Month</th>
    <th>Savings</th>
  </tr>
  <tr>
    <td class="myTd" colspan="2">January</td>
    <td>$100</td>
  </tr>
  <tr>
    <td class="myTd" colspan="2">February</td>
    <td>$100</td>
  </tr>
</table>
<br>

<button>Try it</button>

Note the use of addEventListener() in the above example. This is an unobtrusive event handler bound in JS code, not HTML. It's much better practice over using inline onclick attributes.

How to change getElementbyId to getElementsbyClassName

1 Answers1