A Brief History of JavaScript

JavaScript (which began as Netscape's Mocha) was created in 1995 by Brendan Eich to allow HTML developers to write scripts in their webpages. Read this article to learn about features and functionality that supported the early development of the language. These included a Java-like syntax, basic data types, and objects with classes.

Syntax and Basic Types

SYNTAX

statements like Java
• while, for, if, switch, try/catch, return, break, throw

comments
• use //, avoid /**/

semicolons
• inserted if omitted (yikes!)

declarations
• function scoping with var

functions
• are expressions; closures (yippee!)

var MAX = 10; 
var line = function (i, x) {
     var l = i + " times " + x
          + " is " + (i * x);      
     return l; 
} 

var table =  function (x) {
    for (var i =  1; i <= MAX; i +=  1) {
        console.log(line(i, x));
    } 
} 
// display times table for 3
table(3);

1 times 3 is 3
2 times 3 is 6
3 times 3 is 9
4 times 3 is 12
5 times 3 is 15
6 times 3 is 18
7 times 3 is 21
8 times 3 is 24
9 times 3 is 27
10 times 3 is 30
< undefined
>

BASIC TYPES

primitive types
• strings, numbers, booleans
• operators autoconvert

> 1 + 2
3
> 1 + '2'
"12"
> 1 * 2
2
> 1 * '2'
2

arrays
• can grow, and have holes

funny values
• undefined: lookup non-existent thing
• null: special return value

> a = []
[]
> a[2] = 'hello'
"hello"
> a.length
3
> a[1]
undefined
> a[2]
"hello"
> a[3]
undefined

equality
• use ===, !==

> 1 === 1
true
> 1.0 === 1
true
>'hello' === 'hello'
true
> [] === []
false