JavaScript was created in 1995 by Brendan Eich while he was an engineer at Netscape. JavaScript was first released with Netscape 2 early in 1996. It was originally going to be called LiveScript, but it was renamed in an ill-fated marketing decision that attempted to capitalize on the popularity of Sun Microsystem’s Java language — despite the two having very little in common.

Unlike most programming languages, the JavaScript language has no concept of input or output. It is designed to run as a scripting language in a host environment, and it is up to the host environment to provide mechanisms for communicating with the outside world.

Building Blocks of JS:


The Number type is a double-precision 64-bit binary format IEEE 754 value (numbers between -(253 − 1) and 253 − 1). And where this article and other MDN articles refer to “integers”, what’s usually meant is a representation of an integer using a Number value.

JS contains many functions for numbers implementation :

Math,parseInt,isNaN,isFinite etc.


Strings in JavaScript are sequences of Unicode characters. This should be welcome news to anyone who has had to deal with internationalization. More accurately, they are sequences of UTF-16 code units; each code unit is represented by a 16-bit number. Each Unicode character is represented by either 1 or 2 code units


JavaScript has a boolean type, with possible values true and false (both of which are keywords.) Any value can be converted to a boolean according to the following rules:

  1. false, 0, empty strings (""), NaN, null, and undefined all become false.
  2. All other values become true.

You can perform this conversion explicitly using the Boolean() function:

Boolean('');  // false
Boolean(234); // true


JavaScript objects can be thought of as simple collections of name-value pairs. As such, they are similar to:

  • Dictionaries in Python.
  • Hashes in Perl and Ruby.
  • Hash tables in C and C++.
  • HashMaps in Java.
  • Associative arrays in PHP.


Arrays in JavaScript are actually a special type of object. They work very much like regular objects (numerical properties can naturally be accessed only using [] syntax) but they have one magic property called 'length'. This is always one more than the highest index in the array.

One way of creating arrays is as follows:

var a = new Array();
a[0] = 'dog';
a[1] = 'cat';
a[2] = 'hen';
a.length; // 3


Along with objects, functions are the core component in understanding JavaScript. The most basic function couldn’t be much simpler:

function add(x, y) {
var total = x + y;
return total;

This demonstrates a basic function. A JavaScript function can take 0 or more named parameters. The function body can contain as many statements as you like and can declare its own variables which are local to that function. The return statement can be used to return a value at any time, terminating the function. If no return statement is used (or an empty return with no value), JavaScript returns undefined.

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