A Brief History of JavaScript

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