DEFINITION OF JAVA SCRIPT

• JavaScript (JS) is a lightweight, interpreted, or just-in-time compiled programming language with first-class functions. While it is most well-known as the scripting language for Web pages, many non-browser environments also use it, such as Node.js, Apache CouchDB and Adobe Acrobat. JavaScript is a prototype-based, multi-paradigm, single-threaded, dynamic language, supporting object-oriented, imperative, and declarative (e.g. functional programming) styles.

• Traditionally JavaScript was used inside web browsers such as Mozilla Firefox, Internet Explorer, Chrome, Opera, or Safari. The author would include some JavaScript code in the HTML page the user receives when she visits a web site. That JavaScript code would run in the browser (what we call “client side”, as opposed to running on the web server which is called “server side”).

  We can distinguish 3 major parts of what we usually refer to as “JavaScript”.

• The language itself. This is fairly standard among the various environments, both in the various browsers and in the various server-side environments.
• The DOM API - how the language can interact with the various parts of a web page while in the browser. While in this respect the various browsers are getting closer to each other they still differ. Several libraries, most prominently JQuery, is trying to provide a unified API.
• The server API (or just API) provided by Node.js or one of the other server-side systems.

Input Output “EXAMPLE”

The very first thing we need to learn is how to interact with the JavaScript code running in the browse. There are a number of way JavaScript can display text for the user (output). The most simple one is by using the alert function

• alert :

This will show a pop-up in the browser with the text. (You can click on Try! that will open the specific script in a separate window.) The alert() function is actually rarely used, but it is an easy way to show the use of JavaScript.

• document.write :

In this example we have some text (First line), then the JavaScript code, and then some more text (Last line). The JavaScript code uses the document.write function to change the content of the page. It will embed the html snippet <h1>Hello World</h1> after the “First line”, but before the “Last line”.

• console.log :

Most of the web browsers provide what is called a “JavaScript console”. It is an additional window which is normally not visible, where the browser can print out warnings and errors generated by the execution of the JavaScript code. (E.g. if there is a syntax error in the code.) The developer can also print information to this console using the console.log() call.

In order to see the console you’ll need to open it.