Summary: DOM modification techniques

Posted 2020-11-03 Veritas des Liberty

Modifying an existing element

We covered various ways that you can modify aspects of an existing element:

Modifying attributes

You can set an attribute on an element by setting the property of the same name. For example, to change the src of an <img>:

imgEl.src = "http://www.dogs.com/dog.gif";

In addition, you can also use the setAttribute method, like so:

imgEl.setAttribute("src", "http://www.dogs.com/dog.gif");

If you want to remove an attribute, you should do that with removeAttribute - like to remove the disabled attribute off a button, effectively enabling it:

imgEl.removeAttribute("disabled");

Modifying styles

You can change styles just like how you change attributes, by accessing the style property of the element, and setting the corresponding property. For example, to change the color:

headingEl.style.color = "hotpink";

Remember to "camelCase" the multi-word CSS property names, since hyphens are not valid JS property names:

headingEl.style.backgroundColor = "salmon";

Modifying class names

To add a class to an element, you can set the className property:

mainEl.className = "warning";

That will override any existing classes, so you should do this instead if you just want to add to the list of classes:

mainEl.className += " warning";

In newer browsers, you can use the classList functionality instead:

mainEl.classList.add("warning");

Modifying inner html / text

To completely replace the contents of an element with an arbitrary string of HTML, use innerHTML:

mainEl.innerHTML = "cats are the <strong>cutest</strong>";

If you don‘t need to pass in HTML tags, you should use textContent instead:

mainEl.textContent = "cats are the cutest";

Generally, you should be careful when using either of these 2 properties, because they will also remove event listeners (which we teach in the next tutorial).

Creating elements from scratch

There is a whole set of functions that you can use to create entirely new elements and add them to the page.

To create a new element, use the aptly named createElement:

var imgEl = document.createElement("img");

To append it to the page, call appendChild on the target parent element:

document.body.appendChild(imgEl);

Similarly, you can also use insertBefore, replaceChild, removeChild, and insertAdjacentHTML.