function linkify( selector ) {
if( supports3DTransforms ) {
var nodes = document.querySelectorAll( selector );
for( var i = 0, len = nodes.length; i < len; i++ ) {
var node = nodes[i];
if( !node.className ) {
node.className += ' roll';
}
}
}
}> "hello"
"hello"
> "hello" + " " + "world"
"hello world"
public class HelloWorld {
public static void main(String[] args) {
System.out.println("hello world");
}
}> 1234
1234
> 2 + 2
4
> 3 * 4
12
> 12 / 4
3
> 12 / 5
2.4
> 10 / 3
3.3333333333333335
> 0.1 + 0.2
0.30000000000000004
> 17 % 5 // '%' means "modulus" i.e. remainder
2
> 17.1 % 4.9 // ..slightly weird with non-integers!
2.4000000000000004
> Math.PI // approximately, of course!
3.141592653589793
> Math.pow(2, 8)
256
> Math.pow(8, 2)
64
> Math.sin(0)
0
> Math.sin(90) // it's not in Degrees...
0.8939966636005579
> Math.sin(Math.PI / 2) // it's in Radians
1> hello
ReferenceError: hello is not defined
> var hello // NB: `var` is a statement; it produces no value
undefined
> hello // The var `hello` now exists, with a default value
undefined
> hello = "Greetings!" // Assignment gives it a new value
"Greetings!"
> hello // Which we can now display
"Greetings!"
> greet = hello // Didn't declare this; implicit `var`
"Greetings!"
> var greet = hello // Explicit `var` in the console is annoying
undefined
> greet === hello
true
> hello = "hi"
"hi"
> greet
"Greetings!"
> greet === hello // "===" for sensible equality-testing
false
> greet !== hello // "!==" for sensible not-equality-testing
true
> hello = 99 // A dynamic change of type!
99
> typeof hello
"number"
> typeof greet
"string"
> typeof typeof hello // because "typeof hello" returns a string
"string"> square = function (x) {return x * x;}
function (x) {return x * x;}
> square
function square(x) {return x * x;}
> typeof square
"function"
> square(3)
9
> square(4)
16
> square() // unspecified params have the special val: undefined
NaN // arithmetic on undefined gives "Not A Number" (NaN)
> square(5,6,7,8) // extra params are ignored
25
> timesSelf = square // you can assign functions, like other values
function (x) {return x * x;}
> mystery = function (a, b) {a + b;}
function (a, b) {a + b;}
> mystery(1, 2) // Oops! Forgot "return"; defaults to undefined
undefined
> mystery = function (a, b) {return a + b;}
function (a, b) {return a + b;}
> mystery(1, 2) // Now it should work.
3
> mystery = function (a, b) { // SHIFT-ENTER to cont. on a new line
return a + b;
}
function (a, b) { // SHIFT-ENTER to cont. on a new line
return a + b;
}> sq1 = function (x) {return x * x;} // NB: A function *expression*
function (x) {return x * x;}
> function sq2(x) {return x * x;} // NB: A function *statement*
undefined
> sq2
function sq2(x) {return x * x;}
> sq2.name
"sq2"
> sq1.name
"sq1" // NB: In the past, "" (!)
> sq3 = function name(x) {return x * x;}
function name(x) {return x * x;}
> sq3.name
"name"
> var sq4 = function sq4(x) {return x * x;} // rough equiv of sq2
undefined
> a = []
[]
> a.length
0
> a = ["apple", "banana", "cherry"]
["apple", "banana", "cherry"]
> a.length
3
> a[0]
"apple"
> a[1]
"banana"
> a[2]
"cherry"
> a[3]
undefined
> a[1] = 99
99
> a
["apple", 99, "cherry"]
> a === ["apple", 99, "cherry"] // surprising!
false
> a === a
true
> a[5] = "pear"
"pear"
> a
["apple", 99, "cherry", undefined × 2, "pear"]
> a.length
6
> typeof a
"object"> "hello"[1]
e
> s = "World"
"World"
> s[3]
"l"
> s[3] = "e"
"e"
> s // NB: strings are array-like (and have 'length'), but are immutable!
"World"
> "hello" + " every" + 1
"hello every 1"
> 1 + 2 + "3" + 4 + 5 + "6" // adding with a string "stringifies"
"33456"
> 1 + 2 + "3" + 4 + 5 - "6" // subtracting with a string... oh my god
3339
By Pat Kerr
A high-level overview, which assumes prior familiarity with C++ and Java.
OLD NEWS: I'll be taking my original set of "Computer Game Programming" lectures offline for a little while, but will be publishing them again (with some revisions), week-by-week, for the Autumn 2021 version of the course, starting on August 23rd.
