Manipulating the DOM in JavaScript with innerText and innerHTML

joshtronic

Front-end frameworks are all the rage these days. Working with a virtual DOM, while much more efficient, can be a ton of overhead when all you need to do is tweak a few elements on an existing static page. Fortunately, JavaScript comes with some methods that make it super easy to edit an element’s text as well as the HTML inside of an element.

Take that React, Angular, Vue, and whatever hot new framework I failed to mention!

Getting started

To follow along at home, all you need is a web browser and a page to manipulate.

To make it easy, we can load up any web page, open up our browser’s console and override it with our own HTML document:

document.getElementsByTagName('body')[0].innerHTML = '<div id="gator">Alligators rule!!</div>';

Once you hit enter, the existing page will be completely replaced with a light amount of HTML and a universal truth about everybody’s favorite reptile.

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Editing text

All right, so in the getting started section, we sorta jumped the gun and already used innerHTML to manipulate some elements on the page.

To back it up a small bit, let’s start by changing the text of an element on a page. To do so, we’ll need to select our element and then use innerText to set the content:

document.getElementById('gator').innerText = 'OF COURSE alligators rule!';

Not much to it!

If you wanted to prepend text to an existing string of text, you can use innerText to get the current text and then prepend to it:

const currentText = document.getElementById('gator').innerText;
const nextText = 'Do alligators rule? ' + currentText;
document.getElementById('gator').innerText = nextText;

Appending text is even easier, since we can use +=:

document.getElementById('gator').innerText += ' This definitely true.';

Editing HTML

This is all well and good, but the moment we try to introduce HTML, like wrapping the string in <strong>, things fall apart.

Since innerText works with the text contents of an element, things like HTML tags end up being shown, as if the < and > were encoded as &lt; and &gt;.

No big deal though, when we want to use additional mark up with our string, all we need to do is swap out innerText for innerHTML and be on our way:

document.getElementById('gator').innerHTML = '<strong>OF COURSE</strong> alligators rule!';

And just like innerHTML we can capture the value to prepend to it, and use += to append to it:

const currentHTML = document.getElementById('gator').innerHTML;
const nextHTML = 'Do alligators rule? ' + currentHTML;
document.getElementById('gator').innerHTML = nextHTML;

document.getElementById('gator').innerHTML += ' This definitely true.';

That’s not all, when using innerHTML we can do more than just edit the text of an element. We can also use it to add additional markup, like in the case of an HTML table:

document.getElementById('gator').innerHTML = `
  <table border="1">
    <thead>
      <tr>
        <th>Reptile</th>
        <th>Awesomeness</th>
      </tr>
    </thead>
    <tbody id="tableRows">
      <tr>
        <td>Alligator</td>
        <td>9001</td>
      </tr>
    </tbody>
  </table>
`;

Subsequently, we can use innerHTML to append new rows to the table on the fly:

document.getElementById('tableRows').innerHTML += `
  <tr>
    <td>Snake</td>
    <td>-1</td>
  </tr>
`;

Conclusion

Sure, using innerText and innerHTML doesn’t come close to the power of a front-end framework that’s leveraging a virtual DOM, but hey, it gets the job done.

Fortunately, the days are long gone when innerHTML was the only option available for editing elements with JavaScript. Even though we’ve come a long way, it’s always good to know these things so you don’t go throwing an entire framework at a trivial problem.

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