Javascript Async
JavaScript async refers to the asynchronous nature of JavaScript, allowing code to run independently of the main program flow. It enables non-blocking operations, such as fetching data from a server or handling user input, without halting the entire program. This is achieved through mechanisms like callbacks, promises, and async/await, enhancing the responsiveness and efficiency of JavaScript programs.
3 Key excerpts on "Javascript Async"
eBook - ePubBeginning ReactJS Foundations Building User Interfaces with ReactJS
An Approachable Guide
- Chris Minnick(Author)
- 2022(Publication Date)
- Wiley(Publisher)
...One reason why JavaScript is so fast and the reason that handling asynchronous code correctly is so important is that JavaScript doesn't wait for anything. JAVASCRIPT NEVER SLEEPS JavaScript doesn't have a sleep or wait command. Instead, a JavaScript engine (such as the V8 Engine built into the Chrome web browser and Node.js) starts at the beginning of your script and runs the code as fast as it can, using a single thread. Because JavaScript is single-threaded, it must complete the previous statement before moving on to the next. The call stack in a JavaScript engine is where commands waiting to be executed sit until they can be executed in a First In Last Out (FILO) order. You might be asking yourself at this point how it's possible to do asynchronous tasks (like network requests and caching data) in JavaScript with only one thread. The answer is that although JavaScript itself is single-threaded, the environment in which it runs (your browser or Node.js) is multithreaded. Asynchronous tasks (like network requests) are handled by parts of the browser that are outside of the JavaScript engine, such as the Web APIs, in conjunction with two other parts of the runtime environment outside of JavaScript: the event loop and the callback queue. Consider the following code: console.log("get ready…"); setTimeout(() => { console.log("here it is!"); }, 1000); console.log("end of the code."); The result of running this code in a browser console is shown in Figure 16-1. What's going on here is that when this program starts up, three function calls are added to the call stack to be executed in order. After the first statement is executed and removed from the call stack, JavaScript sees the setTimeout() function, which creates an event that is only indirectly managed by JavaScript. It hands it off to the browser to execute, and then removes it from the call stack...
eBook - ePub- Rob Huddleston(Author)
- 2010(Publication Date)
- Visual(Publisher)
...In most cases, the application being used to run it will be a Web browser. However, many other applications support JavaScript in some form today, so you might also encounter it being used elsewhere. Browser Support Every major modern browser offers full support of JavaScript. Microsoft’s Internet Explorer officially supports ECMAScript, but this in effect means support of JavaScript. You can safely assume that, unless your user has specifically disabled it, all browsers will run your scripts. JavaScript Is Not Java Java is a very powerful object-oriented programming language from Sun Microsystems, whereas JavaScript is a scripting language. Except for the name, they in fact have absolutely nothing in common. Although beginning Web designers commonly confuse the two, care should be taken not to because no help is available for Java that would be useful for JavaScript programming, and vice versa. JavaScript and HTML JavaScript allows developers to achieve many effects not offered by HTML. For example, HTML form controls are extremely limited, and offer little in the way of validation mechanisms to ensure that the data being entered is what is expected. JavaScript allows developers to write as complicated a validation scheme as they need on top of the form. JavaScript can also work in conjunction with CSS to achieve advanced visual effects such as drop-down menus, accordion effects, and much more. Ajax Ajax was developed as a way to allow designers and developers to extend the capabilities offered by HTML and CSS. Most Ajax development is done through prebuilt JavaScript libraries, saving you time in having to rewrite code. The better, more widely adopted libraries focus on good usability and accessibility, and also provide many features such as the ability for JavaScript to refresh only a portion of a Web page...
eBook - ePub- David Karlins, Doug Sahlin(Authors)
- 2012(Publication Date)
- For Dummies(Publisher)
...One is that simple JavaScripts — such as creating alerts (popups), inserting the time, or providing a link that replicates the Back button on a browser — are useful tools and things you can do on your own. The other reason to learn basic JavaScript syntax is that it will help you look at, edit at times, and understand JavaScript that you get from other sources. But the meat of the minibook is showing you how to access, customize, and apply various available packages of JavaScript, including JavaScript libraries (customizable code) and generators (applications and resources that generate JavaScript code without coding). Seeing That JavaScript Is Client-Side Scripting Client-side scripting is basically a technical name for scripts that run in a browser — meaning, in this case, that JavaScripts run in a browser like Internet Explorer, Chrome, Firefox, or Safari. What are the real-world implications of this? It means that the things you do with JavaScript are constrained by its inability to send data to, or grab data from, a remote web server. For example, the scripts (programming) used to handle an order you place for a book at Amazon online or eBay have to run on a server — a massive computer that hosts websites and data. Those scripts combine user input (the order you place) with databases that store the price, shipping costs, inventory stock, and other data needed to fulfill your order. We examine server-side scripting in Book VI. Those are scripts that manage content on servers, like data submitted in a form. Where did that name come from? JavaScript has nothing to do with another programming language called Java. The origin of the name JavaScript is a weird story that can be boiled down to one word: marketing...
