JavaScript Introduction

JavaScript Notes

Defining JavaScript

JavaScript is a scripting or a programming language, allowing developers to perform complex features on web pages. Initially, this language was created for making web pages alive. In JavaScript, the programs are called scripts. One can write them in the HTML of a web page, then it will automatically run once the page loads. At this point, JavaScript is completely different from another language, called Java.

Initially, when JavaScript was created, it was called “LiveScript”. Then, as Java was extremely popular in that period, then it was decided to call it JavaScript to position it relative to Java. But, over the years, JavaScript has transformed into a completely independent language, with its specification, known as ECMAscript, having no relation to Java. Modern JavaScript can both work in the browser and on the server. Basically, it can run on any device that has a specific program known as the JavaScript engine.

What In-browser JavaScript Does

Modern JavaScript is considered a safe programming language. It never provides low-level access to the memory or CPU as it was made for the browsers that don’t require it. The capabilities of this language highly rely on the environment it runs in. For example, Node.js includes functions allowing JavaScript to write and read arbitrary files, implement network requests, and so on. In-browser JavaScript does anything related to web page manipulation.

For example, with in-browser JavaScript, you can do the following:

1. Adding new HTML to the page, changing the content, modifying the styles.
2. Reacting to use actions, running on mouse clicks, key presses, and more.
3. Sending requests over the network to remote servers.
4. Getting and setting cookies, asking questions to visitors, sending messages.
5. Remembering the data on the client-side.

Limitations of In-browser JavaScript

The capabilities of JavaScript are limited for the purpose of keeping the user’s safety. With it, an evil web page can’t access private information or harm the user’s data.

Here are some examples of such restrictions:

• JavaScript has no direct access to OS functions. It can’t read and write arbitrary files on the hard disc, copy or execute them.
• Different windows/tabs don’t recognize each other. JavaSCript from one page is not able to access the other one, in case they are from different sites. It’s known as “Same Origin Policy”.
• JavaScript allows communication over the net to the server from where the page comes from. But, its capability of receiving data from the other site is prohibited. That’s a safety limitation.

What Makes JavaScript Specific

There are at least three perfect things about JavaScript:

1. It supports complete integration with CSS and HTML.
2. It provides straightforward ways of doing simple things.
3. It is supported by almost all the major browsers and is performed by default.
4. It is the exclusive browser technology that encompasses the three great things above.

In modern programming, JavaScript is the most widespread tool that helps to create browser interfaces. It also allows creating mobile applications, servers, and much more. Our JavaScript book consists of several sections that cover all the information you need to learn this unique programming language. Each of the chapters includes both the theory and practical cases to make it easier for beginners to grasp the language.

Javascript History

JavaScript was developed by Brendan Eich in 1995, which appeared in Netscape, a popular browser of that time.

The language was initially called LiveScript and was later renamed JavaScript. There are many programmers who think that JavaScript and Java are the same. In fact, JavaScript and Java are very much unrelated. Java is a very complex programming language whereas JavaScript is only a scripting language. The syntax of JavaScript is mostly influenced by the programming language C.

What is JavaScript?¶

JavaScript is a high-level, dynamic, lightweight, interpreted computer programming language. It’s designed for creating network-centric apps. It has made modern web apps possible— apps with which you can interact directly without doing a page reload for every action. It’s also used in more traditional websites to provide different forms of interactivity and cleverness.

JavaScript is mostly used as a part of web pages. Implementations of JavaScript allow client-side script to interact with the user and make dynamic web pages.

It’s a programming language with object-oriented capabilities. It’s a very strong client-side scripting language. JavaScript is an untyped interpreted programming language that is well-suited to object-oriented and functional programming styles. This programming language will help to make your webpage livelier and more interactive.

Things that make JavaScript great and unique:

1. Full integration with HTML/CSS
2. Simple things are done simply
3. All major browsers support and enabled by default

JavaScript is the only browser technology that includes these three points. Now you understand why it’s the most widespread and powerful tool for creating browser interfaces. JavaScript helps to create servers, mobile applications, games, etc.

Why is it called JavaScript?¶

JavaScript programming language was developed by Brendan Eich in 1995. When JavaScript was created it was known as LiveScript. Netscape changed its name to JavaScript.

Important to know that JavaScript has almost nothing to do with the programming language called Java. The JavaScript name was inspired by marketing considerations. The Java programming language was being heavily marketed and popular when JavaScript was being introduced. After it was adopted outside of Netscape, a standard document was written to describe how the JavaScript language should work. JavaScript has a long way since it becomes a robust, powerful and efficient general-purpose language.

Why to use JavaScript? 

Today, JavaScript is one of the most powerful, popular, and flexible programming languages. It provides dynamic behavior on most websites. JavaScript is used by the overwhelming majority of modern websites. JavaScript interpreters are included in all modern web browsers—on desktops, game consoles, tablets, and smartphones. This makes JavaScript the most ubiquitous programming language in history. JavaScript is a programming language that all Web developers should learn. HTML is needed to specify the content of web pages, CSS to specify the presentation of web pages, and JavaScript to specify the behavior of web pages.

This book will help you master the language.

JavaScript has a lot of advantages like:

• Less server interaction
• Immediate feedback to the visitors
• Increased interactivity
• Richer interfaces

What improvement JavaScript has?¶

There have been several versions of JavaScript programming language. ECMAScript version 3 was the most supported version between 2000 and 2010. Version 4 planned a number of radical improvements and extensions to the language, but it wasn’t done. Then version 5 came out, which made only some uncontroversial improvements, coming out in 2009. Version 6 came out in 2015 and had major updates that included some of the ideas planned for version 4.

Since then JavaScript had new, small updates every year. The fact that JavaScript is evolving means that browsers have to continually keep up. You should know that an older browser may not support every feature offered by JavaScript.

The designers of JavaScript are careful to not make any major changes that could break existing programs. This is done to allow new browsers run old programs. JavaScript is not only used on platforms like Web browsers. Databases like MongoDB and CouchDB, use JavaScript as their scripting and query language. Several platforms for desktop and server programming provide an environment for programming JavaScript outside of the browser (for example Node JS).