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HTML Companion : JavaScript
What is Javascript ?
JavaScript is one of the important programming language of web technologies. It is one of the 3 languages, all web developers must learn :
- HTML : to define the content of web page.
- CSS : to define the structure and stylize web page.
- JavaScript : to define the behavior and add interactive contents in web page.
JavaScript is the scripting language that allows to add interactive and complex things in web pages. A simple HTML web page displays only static content and does not change anything on its own. To add more interesting things like timely content update, interactive maps, 2D/3D graphics, online games etc, you have to use JavaScript. It defines the dynamic behavior of HTML web page. HTML with JavaScript and CSS completes the web technology.
JavaScript is very easy to use and implement because it is integrated with HTML. It is open to use and cross-platform compatible, so it will work on all types of web browsers. It was initially known as LiveScript but Netscape, the company which created it changed its name, probably because it was created as supporting language of java.
JavaScript is the most widely used and deployed programming language in the world. Whether you’re interested in writing front-end client side code, back-end code for servers, or even creation of animation and games, you’ll be able to achieve all of this with JavaScript.
Three building blocks of web technology
1. HTML (Hypertext Markup Language)
2. CSS (Cascading Style Sheet)
3. Javascript
Javascript and APIs
- When writing JavaScript code for web sites , you need to use APIs very soon. APIs — interfaces for modifying and manipulating different environment variables of the web browser and operating system the site is running on, or even data from other web sites or services.
- JavaScript is a scripting language and runs within the browser. It contain some common features like other programming language that allows it to like storing variables, modifying variables, running functions, response to user events (Click, scroll etc) and much more.
- Functionality developed on top of core JavaScript known as APIs(Application Programming Interface) are very easy to use. These are the pre-programmed function and classes which enables user to perform complex task without hard efforts.
There are two types of APIs generally exists for JavaScript
- Web Browser APIs are the APIs which are already inside web browser and are parts of web browser. These APIs are able to read data from computer environment to perform some task. Some examples are Geo-location API, DOM API, Canvas and WebGL API, Audio and Video APIs.
- Third Party APIs are not build into web browser and you need to download them from manufacturers website. Some examples are Google Map API, JQuery API.
How javascript works ?
- If you want to open a web page in your browser, you need to open a tab first. This tab is the execution environment of the browser and code written in web page gets executed here. Code running in one tab cannot affect directly the code running in another tab. This is browser security feature.
- Web browser loads HTML and CSS first and render them on the user screen after that execution of JavaScript starts by the JavaScript Engine of the browser. This make sense, since JavaScript modify HTML and CSS dynamically and without loading it first, JavaScript will throw error.
- When JavaScript engine encounters a JavaScript code written inside a <script> and </script> tag, it execute the code from top to bottom.
- JavaScript is Interpreted language which means the code gets executed line by line and result returns immediately unlike compiled language like c++ in which whole code bock needs to be compiled in machine language first to run.
- JavaScript is a client-side language which runs on user's computer and get interpreted bu user's web browser.
- JavaScript implements dynamic code which means it can change the content of web page dynamically in response to some events.
Version
| Release Date
| Equivalent To
|
|---|---|---|
1.0
| March 1996
| |
1.1
| August 1996
| |
1.2
| June 1997
| |
1.3
| October 1998
| ECMA-262 1st + 2nd edition
|
1.5
| November 2000
| ECMA-262 3rd edition
|
1.6
| November 2005
| 1.5 + array extras + array and string generics + E4X
|
1.7
| October 2006
| 1.6 + Pythonic generators + iterators + let
|
1.8
| June 2008
| 1.7 + generator expressions + expression closures
|
1.8.5
| July 27, 2010
| 1.8.2 + new features for ECMA-262 5th edition compliance
|
When javascript was created ?
JavaScript was created by Brendan Eich in 1995 during his time at Netscape Communications. It was inspired by Java, Scheme and Self.
How do you add JavaScript to your page?
- Internal JavaScript : Internal JavaScript code should be written inside <script> and </script> tags, generally in <head> of the HTML document.
- External JavaScript : External JavaScript code is should be written in a file with extension as ".js" and included in <head> section of HTML page.
Features of JavaScript
- JavaScript is a object-based scripting language.
- Giving the user more control over the browser.
- It Handling dates and time.
- It Detecting the user's browser and OS,
- It is light weighted.
- JavaScript is a scripting language and it is not java.
- JavaScript is interpreter based scripting language.
- JavaScript is case sensitive.
- JavaScript is object based language as it provides predefined objects.
- Every statement in javascript must be terminated with semicolon (;).
- Most of the javascript control statements syntax is same as syntax of control statements in C language.
- An important part of JavaScript is the ability to create new functions within scripts. Declare a function in JavaScript using function keyword.
Limitations of JavaScript
It will not be wise considering javascript as full-fledged programming language. There are some limitations which must be considered
- Client-side Javascript cannot read or write files.
- Javascript cannot be used for networking applications.
- Multithreading and Multiprocessor approach does not apply on javascript.
© 2018 Lalit Kumar
