index

Practice using various methods to update the DOM.

It's important to get comfortable manipulating the Document Object Model (DOM) using JavaScript. This includes creating new elements, updating content, toggling classnames and removing elements.

Quick overview

Here is a quick overview of various DOM manipulation techniques. If you want to find out more about each one you can check their MDN articles.

Accessing elements

You can access elements on the page with the document.querySelector method. This takes any valid CSS selector (like "button" or "#my-id > .my-class:first-child") and searches the DOM for the first match. It returns a DOM element represented as a JS object.

You can access multiple elements with the document.querySelectorAll method. This works in the same way except it returns a NodeList of all matches.

A NodeList is similar to an array but missing most of the usual array methods (it only has .forEach). If you need to use .map/.filter etc you can turn it into an array with Array.from(myList).

Creating elements

You can create a new DOM element with document.createElement. This takes a tag string like "button" and returns the new DOM object.

It's important to note that this object isn't actually on the page yet—it just lives in memory in your JavaScript. To get the element to show up you have to put it inside another element on the page.

You can do this using the parent.appendChild or parent.append methods. The main difference between these is that append works for text and can take multiple items. E.g. myDiv.append(myButton, "some text", myParagraph).

Updating elements

Attributes

Most element attributes are reflected as JavaScript properties on the corresponding DOM object. For example the id attribute can be changed on a DOM object using dot-notation:

const myButton = document.querySelector("button");
// myButton is an object representing the DOM element
// it has properties for all its attributes

myButton.id = "my-id";
// if we change a property the DOM element will be updated

Some attributes are not accessible as object properties. This notably includes ARIA attributes (like aria-label). To change these you must use myEl.setAttribute and myEl.removeAttribute.

This works fine for simple stuff, but for attributes that are lists of strings (like className) it can be awkward. You often want multiple classnames set on an element, but this requires you to manually concatenate strings together.

const myButton = document.querySelector("button");

myButton.className = "btn btn--primary btn--large";
// whoops we overwrote any classes that were already applied

There is a nicer way to manipulate lists like this: the DOMTokenList methods. E.g.

• myElement.classList.add("my-class")

• myElement.classList.remove("my-class")

• myElement.classList.toggle("my-class")

• myElement.classList.contains("my-class")

Content

You can change the text inside an element by setting the textContent property. Be careful though—this will override all existing content, including other DOM elements inside.

You can also use the .append method to add text inside an element. This will work even if there are already other elements inside.

Styles

You can directly add inline styles to an element by setting properties on the myEl.style object. This can get awkward for setting lots of styles, so a simpler way is to add a classname using JS and write the corresponding styles in the CSS instead.

.highlight {
  background-color: yellow;
  padding: 0.5rem;
}

myButton.classList.add("highlight");
// instead of:
// myButton.style.backgroundColor = "yellow"
// myButton.style.padding = "0.5rem" etc

Challenge

Download the starter files and open challenge/dom.js. Your task is to complete as many of these functions as possible. Each should have a comment explaining what it should do.

You can check if each one is working by opening challenge/index.html in your browser. There's a section for each part of the challenge. Don't forget to check the console if something isn't working!