What makes JavaScript special?

JavaScript is the only language that can be used to script within the web browser - therefore it is the only choice when you're making a website with an interactive front-end component.

How's it written?

JavaScript follows the syntax of the Java language (however it's the only thing that it takes from Java), making it similar to C & C++ too. However, unlike these languages, data types are not declared for variables - instead they are inferred at runtime - meaning a variable can change type throughout a script (similar to Python's type system). In technical terms, it has a loose dynamic type system.

                
var helloWorld = "Hello World";
console.log(helloWorld);

var five = 5;
var six = 6;

if (five > six) {
    console.log("Wrong!");
} else {
    console.log("Right!");
}

                
            

Whilst most JavaScript interpreters are loose enough to allow scripts without semi-colons to be written, they should technically always be used at the end of statements (like in the example above). console.log() is simply a print to console statement - like println() in Java, or printf() in C.

History

JavaScript was created in 1995 by Brendan Eich, whilst working at Netscape. He made the language as a 'hack' project within 1 week (source). Since then, the language has been officially standardised by ECMA - making JavaScript an implementation of ECMAScript.

Simple Flow Control

JavaScript includes all of the basic standard flow control statements you'd expect to find in a programming language - namely, if/else if/else statements for conditions, and for and while loops. Below is an example of them in action...

                
// This is a comment!
/* And this is a comment over
    several lines */

// check sanity...
var isItTrue = true;
if (isItTrue) {
    console.log("That was true!!");
} else if (isItTrue === 3) {
    console.log("Wow such number 3");
} else {
    console.log("Not true.");
}

// loop 5 times...
var count = 5;
for (var i = 0; i < count; i++) {
// print the number we're currently at in the loop...
    console.log(count);
}

// to infinity and beyond
var condition = true;
while (condition) {
    console.log("This is really not recommended");
}

                
            

In JavaScript, == checks if two variables have the same value (but they DO NOT have to be of the same type), === checks that they are of the same value AND the same type. This means "5" == 5 is true (because the Number representation of the "5" String is 5), but "5" === 5 is false, because they are of different types. There's more on Data Types in JavaScript next...