concept of server-side JavaScript / JS Framework: NODEJS
- 2. callback function • A callback function is a function which is: • accessible by another function, and • is invoked after the first function if that first function completes • This construct is very useful for asynchronous behaviour where we want an activity to take place whenever a previous event completes.
- 3. • In JavaScript, pass a function as an argument to a function. This function that is passed as an argument inside of another function is called a callback function. For example, <html> <head> <script> function greet(name, callback) { document.write("<h1>" + 'Hi' + ' ' + name + "</h1>"); callback(); } function callMe() { document.write("<h1>" + 'I am callback function' + "</h1>"); } greet('Peter', callMe); </script> </head> <body> </body> </html>
- 4. Benefit of Callback Function • wait for the result of a previous function call and then execute another function call. • In this example, we are going to use the setTimeout() method to mimic the program that takes time to execute, such as data coming from the server. <script> alert(1); setTimeout(() => alert(2), 0); alert(3); </script>
- 5. Two types of programming models- Synchronous and Asynchronous models •Synchronous tasks happen in order — you must finish task one before moving on to the next. •Asynchronous tasks can be executed in any order, or even simultaneously.
- 6. JavaScript •JavaScript is dynamically typed single-threaded interpreted languages for the Web. •Dynamically typed language which means a variable can hold any data type like String or Number in its lifetime and JavaScript interpreter won’t complain about it. •It’s single-threaded which means your JavaScript code runs synchronously or sequentially line by line. It’s interpreted which means you don’t need to compile your JavaScript code.
- 7. JavaScript •JavaScript Interpreter also called a JavaScript Engine. •V8 is the JavaScript engine designed by Google and used in the Google Chrome browser while SpiderMonkey is a JavaScript engine developed by Mozilla for their Firefox browser.
- 8. •Javascript is a single-threaded language, meaning that just one line of code may be run at once. •Javascript is single-threaded because, originally, it was only a web browser scripting language created to serve the needs of a single user on a single window of the browser, eliminating the need for multithreading.
- 9. What is server-side JavaScript? •JavaScript is a single-threaded language, it knows how to get things done one at a time. •It can’t do asynchronous tasks or run JavaScript code in multiple threads for efficiency. •JavaScript is abbreviated as JS or .js/.JS (dot J S) to state that an entity is related to JavaScript, like Node.js or ReactJS or AngularJS.
- 10. What is server-side JavaScript? •JavaScript is used on the web, it needs to be secure. Hence, using JavaScript, you can’t access the computer it is running on, like File System, IO, Networking, etc.
- 11. What is server-side JavaScript? • Web APIs sometimes do their job in separate thread allowing other JavaScript code to run normally while the job is running in the background. • Once the job is done, it then informs the main JavaScript thread. • For example, setTimeout(callback, delay) function is not part of ECMAScript specification, it is provided by the browser to perform an asynchronous operation. The callback function is executed in the main JavaScript thread once delay milliseconds has elapsed.
- 12. how JavaScript runs in a browser
- 13. The concept of server-side JavaScript •You can take any JavaScript engine, wrap inside an application that gives a clean interface to take the user’s JavaScript code and execute it in the JavaScript engine. •You can also provide APIs to perform operations like File System IO, Networking, etc. which do not run on JavaScript engine.
- 14. how JavaScript runs on a server
- 15. Server-side JS Framework •It provide tools and libraries that simplify common web development tasks, •including routing URLs to appropriate handlers, interacting with databases, supporting sessions and user authorization, formatting output (e.g. HTML, JSON, XML), and improving security against web attacks.
- 16. Introduction to Node.js •Node.js is an open-source server side runtime environment built on Chrome's V8 JavaScript engine. •It provides an event driven, non-blocking (asynchronous) I/O and cross-platform runtime environment for building highly scalable server- side applications using JavaScript.
- 17. Node.js •Node.js is nothing but JavaScript running on the server •Node JS is asynchronous and event-driven JavaScript runtime build for scalable network applications. •Although JavaScript in web browser is single thread and synchronous, •Node JS is asynchronous and can use multi threads for I/O or others tasks in background.
- 18. Introduction to Node.js • Node.js is an open-source and cross-platform runtime environment for executing JavaScript code outside a browser. • NodeJS is not a framework and it’s not a programming language. Node.js = Runtime Environment + JavaScript Library
- 19. Needs of Node.js • Enables JavaScript to run outside the browser • Makes use of Google's V8 VM for interpreting JavaScript • Additional modules which simplifies JavaScript development • It’s a runtime and also a library! • JavaScript is an event-driven language, and Node takes this as an advantage to produce highly scalable servers, using an architecture called an event loop. • For Creating High Performance Servers. • Non-Blocking I/O. • Event and Callback based. • Only one Thread and one call stack
- 20. Node JS based applications • Web Application Development. • Hybrid Apps Development. (Both Desktop & Mobile) • API Development. • Chat Applications. • Streaming Services for Video and Audio.
- 21. Node JS Based Web Servers • Netflix • Linkedin • Uber • Paypal • Nasa • Medium • Slack • Twitter • Free Charge • Flipkart Seller
- 22. Node JS Based Desktop Applications • VS Code • Brackets • Atom • MongoDB Compass • Postman • Discord • Dropbox • Figma • Github Desktop • Microsoft Teams • Skype • Wordpress Desktop • Whatsapp for Desktop • Facebook Messenger for Desktop
- 23. Node.js Installation Procedure steps to setup development environment to develop a Node.js application.
- 24. tools/SDK are required for developing a Node.js application on any platform •Node.js •Node Package Manager (NPM) •IDE (Integrated Development Environment) or TextEditor
- 25. Install Node.js on Windows •official web site https://nodejs.org. •It will automatically detect OS and display download link as per your Operating System. •For example, it will display following download link for 64 bit Windows OS.
- 34. Install Node.js on Mac/Linux
- 36. After installation, verify the Node.js installation using terminal window and enter the following command. It will display the version number of Node.js installed on your Mac. $ node -v
- 38. Node.js comes with virtual environment called REPL (aka Node shell). REPL stands for Read-Eval-Print-Loop. It is a quick and easy way to test simple Node.js/JavaScript code. To launch the REPL (Node shell), open command prompt (in Windows) or terminal (in Mac or UNIX/Linux) and type node as shown below. It will change the prompt to > in Windows and MAC.
- 40. If you need to write multi line JavaScript expression or function then just press Enter whenever you want to write something in the next line as a continuation of your code. The REPL terminal will display three dots (...), it means you can continue on next line. Write .break to get out of continuity mode.
- 41. To exit from the REPL terminal, press Ctrl + C twice or write .exit and press Enter.
- 42. JavaScript file • 1. create a sample.js file through text editior / notepad • 2. with in sample.js file - type console.log("Hello World"); 3. Save your file again 4. Open cmd - Move to file location 5. Executing the node filename node sample.js