What is JavaScript?
JavaScript is a programming language that developers use to make interactive webpages. From refreshing social media feeds to displaying animations and interactive maps, JavaScript functions can improve a website's user experience. As a client-side scripting language, it is one of the core technologies of the World Wide Web. For example, when browsing the internet, anytime you see an image carousel, a click-to-show dropdown menu, or dynamically changing element colors on a webpage, you see the effects of JavaScript.
What is JavaScript used for?
Historically, webpages were static, similar to pages in a book. A static page mainly displayed information in a fixed layout and did not do everything we now expect from a modern website. JavaScript emerged as a browser-side technology to make web applications more dynamic. Using JavaScript, browsers could respond to user interaction and change the content layout on the webpage.
As the language matured, JavaScript developers established libraries, frameworks, and programming practices and started using it outside of web browsers. Today, you can use JavaScript for both client-side and server-side development. We provide some common use cases in the following subsections:
Historically, webpages were static, similar to pages in a book. A static page mainly displayed information in a fixed layout and did not do everything we now expect from a modern website. JavaScript emerged as a browser-side technology to make web applications more dynamic. Using JavaScript, browsers could respond to user interaction and change the content layout on the webpage.
As the language matured, JavaScript developers established libraries, frameworks, and programming practices and started using it outside of web browsers. Today, you can use JavaScript for both client-side and server-side development. We provide some common use cases in the following subsections:
How does JavaScript work?
All programming languages work by translating English-like syntax into machine code, which the operating system then runs. JavaScript is broadly categorized as a scripting language, or an interpreted language. JavaScript code is interpreted—that is, directly translated into underlying machine language code by a JavaScript engine. With other programming languages, a compiler compiles the entire code into machine code in a separate step. Thus, all scripting languages are programming languages, but not all programming languages are scripting languages.
JavaScript engine
A JavaScript engine is a computer program that runs JavaScript code. The first JavaScript engines were mere interpreters, but all modern engines use just-in-time or runtime compilation to improve performance.
Client-side JavaScript
Client-side JavaScript refers to the way JavaScript works in your browser. In this case, the JavaScript engine is inside the browser code. All major web browsers come with their own built-in JavaScript engines.
Web application developers write JavaScript code with different functions associated with various events, such as a mouse click or mouse hover. These functions make changes to the HTML and CSS.
Here is an overview of how client-side JavaScript works:
1. The browser loads a webpage when you visit it.
2. During loading, the browser converts the page and all its elements, such as buttons, labels, and dropdown boxes, into a data structure called the Document Object Model (DOM).
3. The browser's JavaScript engine converts the JavaScript code into bytecode. This code is an intermediary between the JavaScript syntax and the machine.
4. Different events, such as a mouse click on a button, trigger the execution of the associated JavaScript code block. The engine then interprets the bytecode and makes changes to the DOM.
5. The browser displays the new DOM.
Server-side JavaScript
Server-side JavaScript refers to the use of the coding language in back-end server logic. In this case, the JavaScript engine sits directly on the server. A server-side JavaScript function can access the database, perform different logical operations, and respond to various events triggered by the server's operating system. The primary advantage of server-side scripting is that you can highly customize the website response based on your requirements, your access rights, and the information requests from the website.
Client-side vs. server-side
The word dynamic describes both client-side and server-side JavaScript. Dynamic behavior is the ability to update the webpage display to generate new content as required. The difference between client-side and server-side JavaScript lies in the way they generate new content. Server-side code dynamically generates new content by using application logic and modifying data from the database. Client-side JavaScript, on the other hand, dynamically generates new content inside the browser by using user-interface logic and modifying the webpage contents that are already on the client. The meaning is slightly different in the two contexts but is related, and both approaches work together to enhance the user experience.
Other than the implementation in dynamic features, another difference between the two JavaScript uses is in the resources the code can access. On the client side, the browser controls JavaScript's runtime environment. The code can access only those resources which the browser permits it to access. For example, it cannot write content to your hard disk unless you click on a download button. On the other hand, server-side functions can access all the server machine's resources as needed.
What are JavaScript libraries?
JavaScript libraries are collections of prewritten code snippets that web developers can reuse to perform standard JavaScript functions. JavaScript library code is plugged into the rest of the project's code on an as-needed basis. If you think of the JavaScript application code as a house, JavaScript libraries are like ready-made furniture that developers can use to improve the functionality of the house.
The following are some common uses of JavaScript libraries:
Data visualization
Data visualization is crucial for users to view statistics, for example, in the admin panel, dashboard and performance metrics.
Libraries such as Chart.js, ApexCharts, and Algolia Places have built-in functions that you can use to create web applications that display data in charts and maps.
DOM manipulation
You can use libraries such as jQuery and Umbrella JS to make web development easy because they provide code for standard website functions such as menu animations, image galleries, buttons, lightboxes, and more.
Forms
Math and text functions
Many web applications have to solve mathematical equations and process dates, times, and text. Instead of sending all such requests to the server, handling some on the client side is more efficient. Web developers do this using JavaScript libraries such as Date.js, Sylvester, and JavaScript URL Library
What are JavaScript frameworks?
Like JavaScript libraries, JavaScript frameworks are a collection of prewritten code snippets that perform different functions and can be reused. However, whereas JavaScript libraries are a specialized tool for on-demand use, JavaScript frameworks are a complete tool set that helps shape and organize any web application. If you think of the JavaScript application code as a house, the JavaScript framework is the blueprint used to build the house.
Here are some example use cases for JavaScript frameworks:
Web and mobile application development
AngularJS is a framework that simplifies the development and testing of web applications, such as e-commerce applications, real-time applications, and video applications. React Native is another framework that supports natively rendered mobile application development for iOS and Android.
Responsive web development
Responsive websites give a consistent user experience across any device. For example, mobile and tablet screens are smaller than desktop and laptop screens. You want the website to display and present data accurately even on the smaller screen, without, for example, cutting off the ends of the website. Using frameworks such as Bootstrap and Ember.js, developers can benefit from responsive design and easily customize a website's look and feel across different platforms.
Server-side application development
Node.js is a server-side, open-source JavaScript framework that runs JavaScript code outside a browser. Developers use this framework to build scalable, fast, and reliable network-based server-side applications. It can handle HTTP requests and data streams, support file systems, and manage multiple backend processes simultaneously.
What are HTML and CSS?
Hypertext Markup Language (HTML) and Cascading Style Sheets (CSS) are two other programming languages that developers use in frontend development. HTML is the basic building block of most webpages. All the paragraphs, sections, images, headings, and text are written in HTML. The content appears on the website in the order it is written in HTML.
CSS is a language of style rules that we use to apply styling to our HTML content. You can use it to design website elements such as background colors, fonts, columns, and borders.
HTML vs. CSS vs. JavaScript
All three languages work together to create a positive user experience on any site. While HTML and CSS can mainly manipulate static content, they can integrate with client-side JavaScript code to dynamically update content too.
For example, the script code block on an HTML page can contain JavaScript within it. The browser can then process both HTML and the internal JavaScript code when the HTML page loads in the browser.What are the benefits of JavaScript?
Easily learn and use
Gain platform independence
Unlike with other programming languages, you can insert JavaScript into any webpage and use it with many other web development frameworks and languages. Once you have written it, you can run JavaScript code on any machine. Thus, JavaScript makes application development platform independent.
Reduce server load
You can use JavaScript to reduce server load and network congestion because it can run logical operations and do a lot of the server's work on the client itself. For example, consider the process of filling out a registration form. JavaScript quickly checks if you have entered a 10-digit number for the mobile phone field. If these requests were sent to the server, your page would reload for every error, making the registration process very slow and tedious.
Improve the user interface
JavaScript creates elegant websites that make it convenient to find and process complex information. Developers apply JavaScript to extend functionality and readability and to make website user interaction more efficient.
Support concurrency
JavaScript can run several different sets of instructions in parallel. On the backend, Node.js can handle and process highly scaled-up server responses without consuming the same amount of bandwidth.
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What are the limitations of JavaScript?
Programming languages use variables as placeholders for actual data values. For example, in a code block, the developer can write x=5 and y=x+1. When the code runs, the computer will automatically change x and y to 5 and 6, respectively, to perform functions on them. Data can be various types, such as a string of text, numbers, or a date. That is why most programming languages allow you to define the variable type. Once the variable type has been defined, it does not change; you cannot store numbers in string variables.
For example, if you tell the program that x and y are numbers and then perform the operation x+y, the computer will know to expect two numbers and add them. On the other hand, if you define x and y as strings, the + operator will append the two strings together to create a longer word.
Weakly typed language
JavaScript is a weakly typed language, which means that it does not allow the programmer to define the variable type. A variable can store any data type at runtime, and operations assume the variable type. The result can also be cast to another data type—for example, an operation might return the result as the string "5" instead of the number 5. This can result in accidental coding mistakes and bugs in the code due to type errors.
What is TypeScript?
TypeScript is a programming language that improves on JavaScript by adding types into the syntax. TypeScript adds additional syntax to JavaScript so that code editor tools can catch coding errors early. At the same time, TypeScript code converts to JavaScript and provides all the same benefits as JavaScript. It also runs in apps and with JavaScript frameworks and libraries.
What is AWS SDK for JavaScript?
AWS SDK for JavaScript is a set of open-source, free-to-use JavaScript libraries that integrate with AWS services. They support API development, higher-level abstractions, and three types of applications:
- JavaScript for browser
- Node.js for server
- React Native for mobile development
The AWS SDK for JavaScript is fully written in TypeScript and then compiled into JavaScript. Thus, you get all the benefits of TypeScript without having to worry about backward compatibility.
You can get started with AWS SDK for Java by reading the code examples and the migration guide or by installing it directly from GitHub.
What is AWS Amplify for JavaScript?
AWS Amplify is a set of purpose-built tools and features that allows frontend web and mobile developers to quickly and easily build full-stack applications on AWS. The Amplify open-source client libraries provide use-case–centric, easy-to-use interfaces across different categories of cloud-powered operations. The Amplify JavaScript libraries are supported for different web and mobile frameworks, including React, React Native, Angular, Ionic, and Vue.js. You can get started by completing the Getting started guide for Amplify JavaScript.