2. What is JavaScript #

Created Wednesday 08 July 2020

Info #

• It is a general purpose programming language.
• Created by NetScape in 1995 to run in the browser.
• It was(is?) a feature for the browser.
• Initially, it was not standardised, just like HTML5, CSS3 for different browsers. This became a nightmare for developers.
• It has now been standardized and is called ECMAScript. JavaScript and ECMAScript are used interchangeably.

What can JavaScript do #

In the browser

1. Create, delete or modify any part of a webpage.
2. React to user input: clicks, pointer movements, key presses.
3. Get and set cookies.
4. Save data in the browser’s “local storage”.
5. Manage requests over the network, but only with the current domain.

Outside the browser(with node) Anything.

1. Flying Drones
2. Robotics

• It can be used for quick development.

What Can’t JS do(in the browser) #

1. Cannot read/write arbitary files to disk, except via the browser’s API, that too for upload/download.
2. Different tabs/windows generally do not know about each other. This is called the “Same Origin Policy”. To work around that, both pages must agree for data exchange and contain a special JavaScript code that handles it. JS can still open new tabs and windows.
3. No access to OS functions.
4. Limited access to Camera/Microphone, provided explicitly by the user via the browser’s API.

• JavaScript’s abilities in the browser are limited for the sake user safety. The aim is to prevent an evil webpage from accessing private information or harming the user’s data.
• No limits exist if JavaScript is used outside of the browser, e.g via node.
• Modern browsers also allow plugin/extensions which may ask for extended permissions.

Why use JavaScript #

• Single language for both front-end and back-end. Lesser things to learns, lesser tools.
• Quite fast and stable.
• Extremely good libraries and frameworks are available - React, Vue, Express
• Easy to learn.
• Portable.

Languages “over” JavaScript #

• JS has been implemented in all browser, with most features.
• JS is efficient, but the syntax is not liked by everyone.
• JS is not suitable for complex apps.
• So people created their own languages, which are transpiled to JS.
• Examples:
  1. CofeeScript - adds “syntactic sugar”, making code short and easy to write.
  2. TypeScript - adds “strict data typing” to make complex systems. By Microsoft.
  3. Dart - Used for mobile apps, but can transpile to JS. By Google.
  4. Brython - a Python transpiler. Supports pure Python development.
  5. Kotlin - modern, concise and safe language that can target the browser or node.

What is node #

JavaScript was experimented with and was found to be quite fast. Consequently, the node interpreter was developed, for running JS as a general purpose programming language outside of the browser.