Javascript why

The updateName code block these types of reusable code blocks are called "functions" asks the user for a new name, and then inserts that name into the paragraph to update the display. If you swapped the order of the first two lines of code, it would no longer work — instead, you'd get an error returned in the browser developer console — TypeError: para is undefined. This means that the para object does not exist yet, so we can't add an event listener to it. Note: This is a very common error — you need to be careful that the objects referenced in your code exist before you try to do stuff to them.

You might hear the terms interpreted and compiled in the context of programming. In interpreted languages, the code is run from top to bottom and the result of running the code is immediately returned. You don't have to transform the code into a different form before the browser runs it. The code is received in its programmer-friendly text form and processed directly from that. Compiled languages on the other hand are transformed compiled into another form before they are run by the computer.

The program is executed from a binary format, which was generated from the original program source code. JavaScript is a lightweight interpreted programming language. The web browser receives the JavaScript code in its original text form and runs the script from that. From a technical standpoint, most modern JavaScript interpreters actually use a technique called just-in-time compiling to improve performance; the JavaScript source code gets compiled into a faster, binary format while the script is being used, so that it can be run as quickly as possible.

However, JavaScript is still considered an interpreted language, since the compilation is handled at run time, rather than ahead of time. You might also hear the terms server-side and client-side code, especially in the context of web development. Client-side code is code that is run on the user's computer — when a web page is viewed, the page's client-side code is downloaded, then run and displayed by the browser. In this module we are explicitly talking about client-side JavaScript.

Server-side code on the other hand is run on the server, then its results are downloaded and displayed in the browser. NET and JavaScript can also be used as a server-side language, for example in the popular Node. Server-side code dynamically generates new content on the server, e. The meaning is slightly different in the two contexts, but related, and both approaches server-side and client-side usually work together. A web page with no dynamically updating content is referred to as static — it just shows the same content all the time.

Let's learn how this works. Note: If your example doesn't seem to work, go through the steps again and check that you did everything right. Did you save your local copy of the starting code as a. Did you enter the JavaScript exactly as shown? JavaScript is case sensitive, and very fussy, so you need to enter the syntax exactly as shown, otherwise it may not work.

Note: You can see this version on GitHub as apply-javascript-internal. This works great, but what if we wanted to put our JavaScript in an external file? Let's explore this now. Note: You can see this version on GitHub as apply-javascript-external. It might look something like this:. Please don't do this, however. In this case the addEventListener function allows you to select all the buttons using one instruction. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 10 years, 8 months ago. Active 10 years, 8 months ago. JavaScript allows users to interact with web pages. There are almost no limits to the things you can do with JavaScript on a web page — these are just a few examples:. Change the color of a button when the mouse hovers over it. Developers can use various JavaScript frameworks for developing and building web and mobile apps.

JavaScript frameworks are collections of JavaScript code libraries that provide developers with pre-written code to use for routine programming features and tasks—literally a framework to build websites or web applications around. Many companies use Node. Beyond websites and apps, developers can also use JavaScript to build simple web servers and develop the back-end infrastructure using Node.

Of course, you can also use JavaScript to create browser games. These are a great way for beginning developers to practice their JavaScript skills. Aside from the unlimited possibilities, there are many reasons for web developers to use JavaScript over other programming languages:.

Either way, this vibrant community and the rise of the web have taken JavaScript place it was never conceived to be. Server-side code was handling the major part of the logic.

Modern browsers now have the capacity to make these interactive and fully-dynamic. A particularity they share with their ancestors, though, is the abstraction of backend development. Logic is handled client-side, directly in the browser, thanks to JavaScript. Modern web trends were born from this new paradigm, like the JAMstack.

I wrote a whole post on the subject that I invite you to read here. Some of the most prominent web applications around today are built using JS. Think Facebook, Gmail, Twitter, and many more. If we use Facebook as an example, JavaScript enables status updates and most user interactivity. These tech giants actually built their own frameworks of JavaScript, and these now allow thousands of devs to build their own web apps.

I also have to mention Vue here that, even if not supported by a tech powerhouse, completes the triad of important JS frameworks.

Other than reducing the amount of time and efforts required for developing JS-based sites and apps, these frameworks helped shape new web experiences. A SPA is a website that interacts with users by dynamically rewriting a page in the browser rather than loading entire new pages from a server, making them behave more like desktop applications.

Yes, the primary use of JavaScript might still be for frontend web development. There were unsuccessful attempts to make JavaScript run server-side from the very beginning. Many thought it would just never become a stable backend language, until the arrival of Node. Today, this JS runtime is a popular tool to power web servers.

This means that JS developers can use Node. I dove deeper in Node. In the past, you would need other languages to develop great mobile applications, like Objective-C for iOS or Java for Android.

This means that you can use mobile devices features, such as the camera or localization to build JS-powered apps. Once again, this opened mobile app development to a more significant number of developers who no longer need to learn a new language. Not only this, but the use of JavaScript in mobile apps even opened up new possibilities to make them even more performant.

Combining the best of the web and the best of apps, PWAs improve reliability, performance, and engagement. They enable impressive new functionalities such as offline navigation. Aforementioned frameworks like Vue.