Understanding the DOM Tree and Nodes
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Introduction

The DOM is usually named the DOM tree, and contains a tree of things called nodes. Thedocument object and modify its properties with the console, and the difference between HTML source code and the DOM.

in the Introduction to the DOM, we went over what the Document Object Model (DOM) is, how to access

In this guide, we are going to review HTML terminology, that is necessary to working together with JavaScript and also the DOM, and we’ll find out about the DOM tree, just what nodes are, and exactly how to determine the absolute most node that is common. Finally, we will move beyond the console and create a program that is javaScript interactively change the DOM.

HTML Terminology

Understanding HTML and JavaScript terminology is vital to learning how to make use of the DOM. Let us quickly review some HTML terminology.

To start, let us have a look at this HTML element.

<a href="index.html">Home</a>

right here we now have an anchor element, that is a hyperlink to index.html.

  • a could be the tag
  • href could be the attribute
  • index.html could be the attribute value
  • Home could be the text.

Everything involving the opening and closing label combined result in the HTML that is entire*****)element.

We’ll be working together with the index.html from past ( that are tutorial*********)

index.html

<!DOCTYPE html>
<html lang="en">

  <head>
    <title>Learning the DOM</title>
  </head>

  <body>
    <h1>Document Object Model</h1>
  </body>

</html>

The easiest option to access a feature with JavaScript is through the id characteristic. Let us include the web link we now have above into our index.html file with an id of nav.

index.html

...
<body>
  <h1>Document Object Model</h1>
  <a id="nav" href="index.html">Home</a>
</body>
...

Load or reload the web page inside web browser screen and appearance at DOM to make sure that the rule happens to be updated.

Weare going to make use of the getElementById() solution to access the element that is entire. The following:( in the console, type*********)

  • document.getElementById('nav');

Output

<a id="nav" href="index.html">Home</a>

We have actually retrieved the element that is entire getElementById(). Now, instead of typing that object and method every right time we should access the nav website link, we are able to put the element into a variable to work alongside it easier.

  • let navLink = document.getElementById('nav');

The navLink variable contains our anchor element. From right here, we are able to effortlessly change characteristics and values. As an example, we are able to alter where in actuality the website link passes changing the href attribute:

  • navLink.href = 'https://www.wikipedia.org';

We may also replace the text content by reassigning the textContent home:

  • navLink.textContent = 'Navigate to Wikipedia';

Now as soon as we see our element, either within the system or by checking the Elements label, we are able to observe how the element happens to be updated.

Output

<a id="nav" href="https://www.wikipedia.org/">Navigate to Wikipedia</a>

This normally mirrored on front-end associated with site.

Updated Link via DOM

Refreshing the web page will return every thing back once again to their values that are original

At this time, you need to discover how to make use of a document solution to access a feature, how exactly to designate a feature to an adjustable, and exactly how to change properties and values within the element.

The DOM Tree and Nodes

All products within the DOM are thought as nodes. There are lots of kinds of nodes, but you will find three ones that are main we make use of frequently:

  • Element nodes
  • Text nodes
  • Comment nodes

whenever an HTML element is a product within the DOM, it really is named an element node. Any text that is lone of an element is a text node, and an HTML comment is a comment node. Thedocument itself is a document node, which is the root of all other nodes.( in addition to these three node types*********)

The DOM contains a tree framework of nested nodes, that is also known as the DOM tree. Maybe you are knowledgeable about an family that is ancestral, which contains moms and dads, kiddies, and siblings. The nodes within the DOM will also be named moms and dads, kiddies, and siblings, based on their reference to other nodes.

To show, create a nodes.html file. We will include text, remark, and element nodes.

nodes.html

<!DOCTYPE html>
<html>

  <head>
    <title>Learning About Nodes</title>
  </head>

  <body>
    <h1>An element node</h1>
    <!-- a remark node -->
    A text node.
  </body>

</html>

The html element node could be the moms and dad node. head and body are siblings, kiddies of html. body contains three youngster nodes, that are all siblings — the kind of node will not replace the degree of which it really is nested.

Note: whenever using an HTML-generated DOM, the indentation associated with source that is HTML will generate numerous empty text nodes, which defintely won't be noticeable from DevTools Elements tab. Learn about Whitespace within the DOM

Identifying Node Type

Every node in a document has a node type, that is accessed through nodeType home. The Mozilla Developer system has an list that is up-to-date of node type constants. Below is a chart of the most node that is common that our company is working together with inside guide.

Node Type Value Example
ELEMENT_NODE 1 The <body> element
TEXT_NODE 3 Text that's not section of a feature
COMMENT_NODE 8 <!-- an comment that is HTML;

In the Elements tab of Developer Tools, you may possibly observe that when you select and emphasize any line within the DOM the worthiness of == $0 can look close to it. This is certainly a really way that is handy access the presently active aspect in Developer Tools by typing $0.

In the system of nodes.html, go through the element that is first the body, that is an h1 element.

DOM Node Type

In the system, have the node type associated with presently chosen node using the nodeType home.

Output

1

With the h1 element chosen, you'd see 1 due to the fact production, which we are able to see correlates to ELEMENT_NODE. Perform some exact same the text and also the remark, plus they shall output 3 and 8 correspondingly.

once you learn how to access a feature, you can observe the node kind without showcasing the aspect in the DOM.

Output

1

In addition to nodeType, you could make use of the nodeValue home to have the worthiness of a text or remark node, and nodeName to have the label title of a feature.

Modifying the DOM with Events

Up as yet, we have just seen how exactly to change the DOM within the system, which we now have seen is short-term; each time the web page is refreshed, the modifications are lost. Inside Introduction towards DOM guide, we utilized the system to upgrade the color that is background of body. We can combine what we've learned throughout this tutorial to create an button that is interactive performs this whenever clicked.

Let's get back to our index.html file and include a button element with an id. We will additionally include a hyperlink to a file that is new a new js directory js/scripts.js.

index.html

<!DOCTYPE html>
<html lang="en">

  <head>
    <title>Learning the DOM</title>
  </head>

  <body>
    <h1>Document Object Model</h1> 
    <button id="changeBackground">Change Background Color</button>

    <script src="http://www.digitalocean.com/scripts.js"></script>
  </body>

</html>

An event in JavaScript is an action the consumer has had. Once the individual hovers their mouse over a feature, or clicks on a feature, or presses a key that is specific the keyboard, these are all types of events. In this case that is particular we wish our key to pay attention and start to become willing to perform an action as soon as the individual clicks onto it. We could repeat this by the addition of an event listener to the key.

Create scripts.js and save yourself it within the brand new js directory. Inside the file, we are going to first get the button element and designate it to a variable.

js/scripts.js

let key = document.getElementById('changeBackground');

Using the addEventListener() technique, we are going to inform the key to pay attention for a simply click, and once perform a function clicked.

js/scripts.js

...
key.addEventListener('click', () => {
  // action goes right here
});

Finally, within the function, we are going to compose the exact same rule from past guide to improve the back ground color to fuchsia.

js/scripts.js

...
document.body.style.backgroundColor = 'fuchsia';

Let me reveal our script:( that is entire*********)

js/scripts.js

let key = document.getElementById('changeBackground');

key.addEventListener('click', () => {
  document.body.style.backgroundColor = 'fuchsia';
});

Once you conserve this file, refresh index.html within the web browser. Click on the key, and also the occasion shall fire.

Modify Background with Events

The back ground color associated with web page changed to fuchsia as a result of event that is javaScript

Conclusion

In this guide, we reviewed terminology which will let us comprehend and change the DOM. We discovered the way the DOM is organized as a tree of nodes which will often be HTML elements, text, or commentary, and now we created a script that could enable a person to change a web site and never having to code that is manually type the designer system.

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