2. JavaScript is a stripped down version of Java
JavaScript does not exist outside browsers
JavaScript is inconsistent and buggy
JavaScript is not object-orientated
3. Birth of Mocha, then rename to LiveScript
Netscape and Sun collaboration for Java in
browsers;
LiveScript gets renamed to JavaScript
IE team reverse engineers JavaScript to JScript
Browser war begins
Standardization of JavaScript at ECMA;
ECMAScript becomes the official name
Rise of Ajax
JavaScript libraries emerge
ECMAScript 5
8. Number
String
Boolean
Object
Function
Array
Date
RegExp
Null
Undefined
9. Only one number type
No integers
64-bit floating point IEEE-754 (aka “Double”)
Numbers are Objects
10. (a + b) + c === a + (b + c)
Produces false for some values of a, b, c.
Integers under 9007199254740992 (9
quadrillion) are ok.
9007199254740992 === 9007199254740992 + 1
11. a = 0.1;
b = 0.2;
c = 0.3;
(a + b) + c === a + (b + c)
> false
12. Special number: Not a Number
Result of undefined or erroneous operations
Toxic: any arithmetic operation with NaN as an
input will have NaN as a result
NaN is not equal to anything, including NaN
NaN === NaN is false
NaN !== NaN is true
13. A sequence of 0 or more 16-bit Unicode
characters
No separate character type
Characters are represented as strings with length
of 1
Strings are immutable
Similar strings are equal ( === )
String literals can use single or double quotes with
escapement.
Strings are Objects
14. > "hello".charAt(0)
h
> "hello, world".replace("hello",
"goodbye")
goodbye, world
> "hello".toUpperCase()
HELLO
15. null = deliberately no value
undefined = no value assigned yet
Variables declared but not initialized
Object/array members that don't exist
16. Boolean type: true or false
Everything else is “truthy” or “falsy”
0, "", NaN, null and undefined are falsy
Everything else is truthy
Boolean operations: &&, || and !
17. Simple key-value pairs, like:
HashMaps in Java
Associative arrays in PHP
Key is a string; value can be anything
Key is unique within an object
18. var obj = new Object();
Or
var obj = {};
These are semantically equivalent; the second is
called object literal syntax and is more
convenient.
19. obj.name = "My Name"
var name = obj.name;
Or
obj["name"] = "My Name";
var name = obj["name"];
Semantically equivalent; the second uses strings
so can be decided at run-time (and can be
used for reserved words)
21. Iterate over the keys of an object:
var obj = { 'name': 'Simon', 'age': 25
};
for (var attr in obj) {
alert (attr + ' = ' + obj[attr]);
}
Not to be used with Arrays
22. A special type of object: Keys are whole numbers,
not strings.
Use [] syntax, just like objects
> var a = new Array();
> a[0] = "dog";
> a[1] = "cat";
> a[2] = "hen“;
> a.length
3
No such thing as “Associative Arrays”
23. More convenient notation:
> var a = ["dog", "cat", "hen"];
> a.length
3
var a = [10, "dog", false, "elephant"];
(you can have mixed content in arrays)
24. > var a = ["dog", "cat", "hen"];
> a[100] = "fox";
> a.length
101
typeof a[90] == 'undefined'
array.length is always one more than the
highest index
The safest way to append new items is:
a[a.length] = item;
25. New variables are declared using the var
keyword:
var a;
var name = "my name";
If you declare a variable without assigning it to
anything, its value is undefined.
If you forget the var, you get a global variable.
Never, ever do this – not even if you mean it.
26. Global variables are visible everywhere
Blocks do not have scope
Variables defined inside blocks are hoisted to
the top and are visible outside the block
Functions have scope
Variables defined inside function are visible
throughout the function and its inner functions
27. var a;
//...
function F() {
var b;
//...
function N() {
var c;
//...
};
}
28. Three different purposes of functions:
as sub-routine / procedure
as lambda (a block of executable code)
as object constructor
Functions are first-class:
can be assigned to a variable
can be passed as argument to any function
can be returned from any function
can be a member of any object
can be created at run time
Functions can be created inside another function
29. function add(x, y) {
var total = x + y;
return total;
}
var add = function(x, y) {
var total = x + y;
return total;
};
var add = function some_func(x, y) {
var total = x + y;
return total;
};
If nothing is explicitly returned, return value is undefined
30. Parameters: “They’re more like... Guidelines”
Missing parameters are treated as undefined:
> add()
NaN // addition on undefined
You can pass in more arguments than
expected:
> add(2, 3, 4)
5 // added the first two; 4 was ignored
31. The arguments special variable provides access to arguments as an
array-like object
function add() {
var sum = 0;
for (var i = 0, j = arguments.length; i < j; i++) {
sum += arguments[i];
}
return sum;
}
> add(2, 3, 4, 5)
14
33. var add = function(x) {
return function(y) {
return x + y;
};
};
34. function Person(name) {
this.name = name;
this.getName = function() {
return this.name;
};
}
var person = new Person("some one");
person.getName();
> some one
