JavaScript has changed the web development field, enabling developers to create dynamic and interactive web applications. Firstly, with the change in technology and user demand, JavaScript has emerged as a crucial programming language for building modern applications. In this blog post, we will explore the pivotal role of JavaScript in the development of web applications and delve into its various features and capabilities.
What is Javascript?
JavaScript was initially created to “make web pages alive”. The programs in this language are called scripts. They can be written right in a web page’s HTML and run automatically as the page loads. Scripts are provided and executed as plain text. They don’t need special preparation or compilation to run. In this aspect, JavaScript is very different from another language called Java.
Today, JavaScript can execute not only in the browser, but also on the server, or actually on any device that has a special program called the JavaScript engine. The browser has an embedded engine sometimes called a “JavaScript virtual machine”. Different engines have different “codenames”. For example:
- V8 – in Chrome, Opera and Edge.
- SpiderMonkey – in Firefox.
- …There are other codenames like “Chakra” for IE, “JavaScriptCore”, “Nitro” and “SquirrelFish” for Safari, etc.
- The terms above are good to remember because they are used in developer articles on the internet. We’ll use them too. For instance, if “a feature X is supported by V8”, then it probably works in Chrome, Opera and Edge.
What can in-browser JavaScript do?
Modern JavaScript is a “safe” programming language. It does not provide low-level access to memory or the CPU, because it was initially created for browsers which do not require it. JavaScript’s capabilities greatly depend on the environment it’s running in. For instance, Node.js supports functions that allow JavaScript to read/write arbitrary files, perform network requests, etc. In-browser JavaScript can do everything related to webpage manipulation, interaction with the user, and the webserver. For instance, in-browser JavaScript is able to:
- Add new HTML to the page, change the existing content, modify styles.
- React to user actions, run on mouse clicks, pointer movements, key presses.
- Send requests over the network to remote servers, download and upload files (so-called AJAX and COMET technologies).
- Get and set cookies, ask questions to the visitor, show messages.
- Remember the data on the client-side (“local storage”).
What can’t in-browser JavaScript do?
JavaScript’s abilities in the browser are limited to protect the user’s safety. The aim is to prevent an evil webpage from accessing private information or harming the user’s data. Examples of such restrictions include:
- JavaScript on a webpage cannot read/write arbitrary files on the hard disk, copy them, or execute programs, and it lacks direct OS access. Modern browsers allow limited file access only with user actions like “dropping” a file into the browser or selecting it via an input tag. JavaScript can interact with devices like cameras/microphones but requires explicit user permission.
- Different tabs/windows generally don’t know about each other unless one uses JavaScript to open the other. Even then, the Same Origin Policy prevents JavaScript from accessing other pages if they come from different sites, domains, protocols, or ports, ensuring user safety.
- JavaScript can communicate with the server of the current page but has limited ability to receive data from other sites/domains without explicit agreement via HTTP headers. This is another safety measure.
- JavaScript can easily communicate over the net to the server where the current page came from. But its ability to receive data from other sites/domains is crippled. Though possible, it requires explicit agreement (expressed in HTTP headers) from the remote side. Once again, that’s a safety limitation.
- Such limitations do not exist if JavaScript is used outside of the browser, for example on a server. Modern browsers also allow plugins/extensions which may ask for extended permissions.
What makes JavaScript unique?
There are at least three great things about JavaScript:
- Full integration with HTML/CSS.
- Simple things are done simply.
- Supported by all major browsers and enabled by default.
JavaScript is the only browser technology that combines these three things. That’s what makes JavaScript unique. That’s why it’s the most widespread tool for creating browser interfaces. That said, JavaScript can be used to create servers, mobile applications, etc.
Languages “over” JavaScript
The syntax of JavaScript does not suit everyone’s needs. Different people want different features. That’s to be expected, because projects and requirements are different for everyone. So, recently a plethora of new languages appeared, which are transpiled (converted) to JavaScript before they run in the browser. Modern tools make the transpilation very fast and transparent, actually allowing developers to code in another language and auto-converting it “under the hood”. Examples of such languages:
- CoffeeScript is “syntactic sugar” for JavaScript. It introduces shorter syntax, allowing us to write clearer and more precise code. Usually, Ruby devs like it.
- TypeScript is concentrated on adding “strict data typing” to simplify the development and support of complex systems. It is developed by Microsoft.
- Flow also adds data typing, but in a different way. Developed by Facebook.
- Dart is a standalone language that has its own engine that runs in non-browser environments (like mobile apps), but also can be transpiled to JavaScript. Developed by Google.
- Brython is a Python transpiler to JavaScript that enables the writing of applications in pure Python without JavaScript.
- Kotlin is a modern, concise and safe programming language that can target the browser or Node.
There are more. Of course, even if we use one of these transpiled languages, we should also know JavaScript to really understand what we’re doing.
JavaScript has become an indispensable tool in modern web application development. Its versatility, interactivity, and cross platform compatibility empower developers to create dynamic, responsive, and user friendly applications. With JavaScript frameworks, libraries, and emerging technologies, the possibilities for web application development are continually expand. Such as the web evolves, JavaScript remains at the forefront, enabling developers to build powerful and engaging applications that cater to the needs of today’s digital way.
If you are new to programming and want to learn Javascript, You can refer to our blog Learning Javascript – Baby Steps.
“written right in a web page’s HTML ” check this