Javascript DOM Events
JavaScript DOM events are actions that occur in the Document Object Model (DOM) of a web page, such as a user clicking a button or hovering over an element. These events can be programmed to trigger specific JavaScript functions, allowing for interactive and dynamic web page behavior. Event handling is a fundamental aspect of web development and is essential for creating responsive and engaging user interfaces.
5 Key excerpts on "Javascript DOM Events"
eBook - ePubExploring Web Components
Build Reusable UI Web Components with Standard Technologies
- Andrea Chiarelli(Author)
- 2020(Publication Date)
- BPB Publications(Publisher)
...As a JavaScript developer, you know how to deal with events. Anyway, before going into event management for web components, let's recap in this section a few notions about events, just be on the same page. Events allow us to define the behavior of our application when the user interacts with it or when something happens inside the system, basically the DOM, or the application itself. To intercept events, we usually use a handler or listener, which is a function associated with a specific event. You have three ways to associate a handler with an event: Using the addEventListener() method in your JavaScript code Using specific attributes in the HTML markup Using specific properties of the HTML element Using attributes and properties to assign event handlers to an HTML element is quite straightforward and handy. However, the addEventListener() method provides you with a more advanced way to manage events. For example, it allows you to add multiple handlers to the same event. It also allows you to control how the handler fits in the event propagation flow, as we will see in a moment. When an event triggers, an object containing some details about the event itself is passed to the handler. You can use this object in your handler, as shown in the following example: const button = document.getElementById("myButton"); button.addEventListener("click", (event) => { console.log(‘You clicked the button “${event.target.innerHTML}”‘); }); In this example, we used the target property of the event object. It represents the HTML element the event fired on. We used the innerHTML property of this HTML element to show the text of the clicked button on the browser's console. When an event occurs, it goes through the DOM following a specific path...
eBook - ePubBeginning ReactJS Foundations Building User Interfaces with ReactJS
An Approachable Guide
- Chris Minnick(Author)
- 2022(Publication Date)
- Wiley(Publisher)
...It converts HTML, styles, and content into nodes that can be operated on using JavaScript.If you've ever used thegetElementByIdfunction or set theinnerHTMLof an element, you've interacted with the DOM using JavaScript. Changes to the DOM cause changes to what you see in your web browser, and updates made in the web browser (such as when you enter data into a form) cause changes to the DOM.Compared to other kinds of JavaScript code, DOM manipulation is slow and inefficient. This is because whenever the DOM changes, the browser has to check whether the change will require the page to be redrawn and then the redrawing has to happen.Adding to the difficulty of DOM manipulation is that the DOM's functions aren't always easy to use and some of them have excessively long names likeDocument.getElementsByClassName. For both of these reasons, many different JavaScript DOM manipulation libraries have been created. The single most popular and widely used DOM manipulation library of all time wasjQuery. It gave web developers an easy way to make updates to the DOM, and that changed the way we build user interfaces on the web.Although jQuery made DOM manipulation easier, it left it up to programmers to program specifically when and how changes to the DOM would happen. The result was often inefficient user interfaces that were slower both to download and to respond to user interactions because of their use of jQuery. As a result, jQuery got a reputation for being slow.When the engineers at Facebook designed React, they decided to take the details of how and when the DOM is modified out of the hands of programmers. To do this, they created a layer between the code that the programmer writes and the DOM...
eBook - ePub- David Karlins, Doug Sahlin(Authors)
- 2012(Publication Date)
- For Dummies(Publisher)
...JavaScript J avaScript is the main source of interactivity and animation in web pages. And of even greater value, it helps visitors interact with objects. They can click a button, scroll a drop-down menu, choose an option from a drop-down menu, and so on — all user-initiated events trigger an action. That action might be launching a slideshow, or opening a new browser window, or a form being validated (the data a user enters is tested before that data is sent to a server). As such, JavaScript is the third leg of the basic building blocks of modern, inviting, dynamic websites, along with HTML (which we cover in Book III, and throughout this minibook) and CSS (which we cover in Book IV). Understanding the Role of JavaScript As you peruse the web to identify the source of various content you want to include in your site, train your brain (and eye) to identify JavaScript objects. You’ll find them everywhere. For example, basic fly-out menus, like the one in Figure 1-1 from eBay, are typically created with JavaScript. Drop-down menus and JavaScript There are other techniques for creating animated drop-down menus. For example, some are created using only CSS (style sheets). But JavaScript drop-down menus are the most widely implemented, powerful, and accessible in a wide variety of browsing environments. The JavaScript code that makes drop-down menus work is stored in files with a.js filename extension. If you look at the source code for a website that includes JavaScript, you most likely won’t see the hundreds or thousands of lines of JavaScript code that make drop-down menus and other animated, interactive elements do their thing...
eBook - ePub- Mike McGrath(Author)
- 2020(Publication Date)
- In Easy Steps Limited(Publisher)
...‘ <br> ’ Then, add statements to create buttons in the paragraphs info.innerHTML += ‘ <button onclick=”history.back()”>Back</button> ’ info.innerHTML += ‘<button onclick=”history.forward()”>Forward</button>’ Save the HTML document and JavaScript script file in the same folder, then clear your browser’s history To clear the browser history in the Google Chrome browser, click the button, then select More tools, Clear browsing data, and click the Clear data button. Open the first page to see the initial history length is 1 Click a link to load the third page and see the history length increase to 2 Click the Back button to return to the first page but see the history length remain the same as 2 The URLs are stored in the history object array elements in a protected manner so they cannot be retrieved as strings. In this example, each URL only gets added to the history array when moving to a different page by clicking on a link. The back(), forward(), and go() methods simply select an element in the history array so do not change its length property. Summary • The Document Object Model (DOM) is a hierarchical tree representation of all components of a web page. • The window object is the top level in the DOM hierarchy and has properties describing the browser window. • The screen object is a child of the window object and has properties describing the screen dimensions and color depth. • The window object has scrollBy() and scrollTo() methods and scrollX and scrollY properties that specify the scroll position. • Dialog messages can be displayed using the window object’s alert(), confirm(), and prompt() methods. • A pop-up window can be created using the window object’s open() method, but may be obstructed by a pop-up...
eBook - ePub- Sean McManus(Author)
- 2014(Publication Date)
- In Easy Steps Limited(Publisher)
...8 JavaScript for interactive pages JavaScript enables you to make your web pages interactive. You can check that forms have been completed correctly, update the screen with text or photos; display randomly chosen special offers; and add sophisticated animation and formatting effects to your pages. In this chapter, you’ll learn the basics and discover some handy code you can adapt for your website. What is JavaScript? How to add JavaScript Creating functions Responding to user actions Showing and hiding content How it works Adding a toggle routine Simple form validation Checking text boxes More advanced form tests Customizing by date Opening new windows Adding random content Adding a photo slideshow Saving time with jQuery 2 quick jQuery examples What is JavaScript? While HTML is used to describe the structure of your content, and CSS lets you describe its appearance, JavaScript gives you the power to make the computer perform actions. It is a simple programming language that you can use to make your web page interactive. For security reasons, JavaScript is limited to working within the browser. That means that it can’t interfere with the website visitor’s computer, and access the hard disk, for example. You can, for example: • Update the screen contents after the page has downloaded. You might add new information that has become available since the web page first downloaded, or might show additional information that the user requests. Webmail service Gmail uses JavaScript to show you new messages that come in, without you having to refresh the web page, for example. • Make it easier for visitors to use forms by checking for any errors before the form information is sent to the server. You can provide immediate feedback so that users don’t waste time waiting for the server to respond. • Hide or reveal web page content...
