A Re-Introduction to JavaScript

Slideshow Transcript

1. Slide 1: http://www.flickr.com/photos/tomsly/93947243/ - thomas_sly A (Re)-Introduction to JavaScript Simon Willison ETech, March 6th, 2005 1 1
2. Slide 2: Coming up... • Numbers, Strings and things • Variables and Operators • Control Structures • Objects and Arrays • Functions • Object constructors and inheritance • Inner functions and closures • Memory Leaks... and more 2 2
3. Slide 3: Book recommendation • JavaScript: The Definitive Guide – by David Flanagan • Comprehensive overview of the language in the first 20 chapters • New edition out later this year 3 3
4. Slide 4: More book recommendations • For practical applications of this stuff: 4 4
5. Slide 5: You will need... • Firefox – Any web browser can run JavaScript, but Firefox has the best tools for developers • Jesse Ruderman's 'shell' tool – http://www.squarefree.com/shell/ • A text editor may come in handy too 5 5
6. Slide 6: In the words of its creator JavaScript was a rushed little hack for Netscape 2 that was then frozen prematurely during the browser wars, and evolved significantly only once by ECMA. So its early flaws were never fixed, and worse, no virtuous cycle of fine-grained community feedback in the form of standard library code construction, and revision of the foundational parts of the language to better support the standard library and its common use-cases, ever occurred. 6 http://weblogs.mozillazine.org/roadmap/archives/2006/02/js_and_python_news.html 6
7. Slide 7: http://www.flickr.com/photos/kingcoyote/93491484/ - King Coyote The History of JavaScript (in 30 seconds) 7 7
8. Slide 8: JavaScript was... Invented by Brendan Eich in 1995 for Netscape; originally called LiveScript, current name being an ill-fated marketing decision to tie in with Sun's newly released Java; adapted by Microsoft as JScript for IE 3 in 1996; standardised as ECMAScript in 1997; sort-of included in Flash as ActionScript; updated to ECMAScript 3rd edition in 1998 8 8
9. Slide 9: Not quite general purpose • No direct concept of input or output • Runs within a host environment – Web browser – Adobe Acrobat – Photoshop – Windows Scripting Host – Yahoo! Widget Engine – and more... 9 9
10. Slide 10: http://www.flickr.com/photos/olivepress/11223013/ - Brian Sawyer Syntax 10
11. Slide 11: Reserved words break else new var case finally return void catch for switch while continue function this with default if throw delete in try do instanceof typeof abstract enum int short boolean export interface static byte extends long super char final native synchronized class float package throws const goto private transient debugger implements protected volatile double import public 11 11
12. Slide 12: Style recommendations • Avoid semi-colon insertion like the plague ;;; friends • Declare variables religiously with 'var' • Global variables are evil. Avoid them if you can. • Indent consistently 12 12
13. Slide 13: http://www.flickr.com/photos/kvitsh/64919318/ - K'vitsh / Heather Hutchinson Types 13 13
14. Slide 14: JavaScript types • Numbers • Strings • Booleans • Functions • Objects 14 14
15. Slide 15: JavaScript types (improved) • Number • String • Boolean • Object – Function – Array – Date – RegExp • Null • Undefined 15 15
16. Slide 16: http://www.flickr.com/photos/51035555243@N01/72778694/ - Thomas Hawk Numbers 16 16
17. Slide 17: Numbers • \"double-precision 64-bit format IEEE 754 values\" • No such thing as an integer 0.1 + 0.2 = 0.30000000000000004 3 + 5.3 28 % 6 etc... • Math namespace for advanced operations 17 17
18. Slide 18: Math stuff • Math.PI, Math.E, Math.LN10, Math.LN2, Math.LOG10E, Math.SQRT1_2, Math.SQRT2 • Math.abs(x), Math.acos(x), Math.asin(x), Math.atan(x), Math.atan2(y, x), Math.ceil(x), Math.cos(x), Math.exp(x), Math.floor(x), Math.log(x), Math.max(x, ..), Math.min(x, ..), Math.pow(x, y), Math.random(), Math.round(x), Math.sin(x), Math.sqrt(x), Math.tan(x) 18 18
19. Slide 19: parseInt (and parseFloat) • parseInt converts a string to a number > parseInt(\"123\"); 123 > parseInt(\"010\"); Always specify the base 8 • !? > parseInt(\"010\", 10); 10 > parseInt(\"11\", 2) 3 19 19
20. Slide 20: NaN and Infinity > parseInt(\"hello\", 10) NaN • NaN is toxic > NaN + 5 NaN > isNaN(NaN) true • Special values for Infinity and -Infinity: >1/0 > -1 / 0 Infinity -Infinity 20 20
21. Slide 21: http://www.flickr.com/photos/solarider/53494967/ - solarider Strings 21 21
22. Slide 22: Strings • Sequences of characters • Sequences of unicode characters (16 bit) \"\\u0020\" • A character is a string of length 1 > \"hello\".length 5 • Strings are objects! 22 22
23. Slide 23: String methods > \"hello\".charAt(0) h > \"hello, world\".replace(\"hello\", \"goodbye\") goodbye, world > \"hello\".toUpperCase() HELLO 23 23
24. Slide 24: More string methods s.charAt(pos) s.charCodeAt(pos) s.concat(s1, ..) s.indexOf(s1, start) s.lastIndexOf(s1, startPos) s.localeCompare(s1) s.match(re) s.replace(search, replace) s.search(re) s.slice(start, end) s.split(separator, limit) s.substring(start, end) s.toLowerCase() s.toLocaleLowerCase() s.toUpperCase() s.toLocaleUpperCase() 24 24
25. Slide 25: Null and undefined • null = deliberately no value • undefined = no value assigned yet – Variables declared but not initialised – Object/array members that don't exist – (More on this later) 25 25
26. Slide 26: Booleans • Boolean type: true or false • Everything else is \"truthy\" or \"falsy\" • 0, \"\", NaN, null, undefined are falsy • Everything else is truthy • Boolean operations: &&, || and ! • Convert any value to it's boolean equivalent by applying not twice: > !!234 > !!\"\" true false 26 26
27. Slide 27: http://www.flickr.com/photos/antmoose/71277315/ - antmoose / Anthony M. Variables and operators 27 27
28. Slide 28: Variable declaration • New variables in JavaScript are declared using the var keyword: var a; var name = \"simon\"; • 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. 28 28
29. Slide 29: Operators Numeric operators: +, -, *, / and % • Compound assignment operators: +=, -=, *=, /=, %= • Increment and decrement: a++, ++a, b--, --b • String concatenation: > \"hello\" + \" world\" hello world 29 29
30. Slide 30: Type coercion > \"3\" + 4 + 5 345 > 3 + 4 + \"5\" 75 • Adding an empty string to something else converts it to a string. 30 30
31. Slide 31: Comparison • >, <, >=, <= work for numbers and strings • Equality tests use == and != ... sort of > \"dog\" == \"dog\" true > 1 == true true • === and !== avoid type coercion > 1 === true false > true === true true 31 31
32. Slide 32: The typeof operator typeof v number 'number' string 'string' boolean 'boolean' function 'function' object 'object' array 'object' null 'object' undefined 'undefined' 32 32
33. Slide 33: http://www.flickr.com/photos/setre/8825214/ - setre Control structures 33 33
34. Slide 34: if statements var name = \"kittens\"; if (name == \"puppies\") { name += \"!\"; } else if (name == \"kittens\") { name += \"!!\"; } else { name = \"!\" + name; } name == \"kittens!!\" 34 34
35. Slide 35: while and do-while while (true) { // an infinite loop! } do { var input = get_input(); } while (inputIsNotValid(input)) 35 35
36. Slide 36: for loops for (var i = 0; i < 5; i++) { // Will execute 5 times } 36 36
37. Slide 37: switch statement • Multiple branches depending on a number or string switch(action) { case 'draw': drawit(); break; case 'eat': eatit(); break; default: donothing(); } 37 37
38. Slide 38: fall through switch(a) { case 1: // fallthrough case 2: eatit(); break; default: donothing(); } • Deliberate labelling of fall through is good practise 38 38
39. Slide 39: Switch expressions • Expressions are allowed • Comparisons take place using === switch(1 + 3): case 2 + 2: yay(); break; default: neverhappens(); } 39 39
40. Slide 40: Short-circuit logic • The && and || operators use short-circuit logic: they will execute their second operand dependant on the first. • This is useful for checking for null objects before accessing their attributes: var name = o && o.getName(); • Or for setting default values: var name = otherName || \"default\"; 40 40
41. Slide 41: The tertiary operator • One-line conditional statements var ok = (age > 18) ? \"yes\" : \"no\"; • Easy to abuse; use with caution 41 41
42. Slide 42: Exceptions try { // Statements in which // exceptions might be thrown } catch(error) { // Statements that execute // in the event of an exception } finally { // Statements that execute // afterward either way } throw new Error(\"An error!\"); throw \"Another error!\"; 42 42
43. Slide 43: http://www.flickr.com/photos/spengler/51617271/ - Andreas D. Objects 43 43
44. Slide 44: Objects • Simple name-value pairs, as seen in: – Dictionaries in Python – Hashes in Perl and Ruby – Hash tables in C and C++ – HashMaps in Java – Associative arrays in PHP • Very common, versatile data structure • Name part is a string; value can be anything 44 44
45. Slide 45: Basic object creation var obj = new Object(); • Or: var obj = {}; • These are semantically equivalent; the second is called object literal syntax and is more convenient. 45 45
46. Slide 46: Property access obj.name = \"Simon\" var name = obj.name; • Or... obj[\"name\"] = \"Simon\"; var name = obj[\"name\"]; • Semantically equivalent; the second uses strings so can be decided at run-time (and can be used for reserved words) 46 46
47. Slide 47: Object literal syntax var obj = { name: \"Carrot\", \"for\": \"Max\", details: { color: \"orange\", size: 12 } } > obj.details.color > obj[\"details\"][\"size\"] orange 12 47 47
48. Slide 48: for (var attr in obj) • You can iterate over the keys of an object: var obj = { 'name': 'Simon', 'age': 25}; for (var attr in obj) { print (attr + ' = ' + obj[attr]); } • Don't attempt this with arrays (coming up next). There are safer ways of iterating over them. 48 48
49. Slide 49: http://www.flickr.com/photos/adrian_s/28567268/ - waffler / Adrian Sampson Arrays 49 49
50. Slide 50: Arrays • 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 50 50
51. Slide 51: Array literals • More convenient notation: > var a = [\"dog\", \"cat\", \"hen\"]; > a.length 3 51 51
52. Slide 52: array.length > 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; 52 52
53. Slide 53: Array iteration for (var i = 0; i < a.length; i++) { // Do something with a[i] } • Improve this by caching a.length at start: for (var i = 0, j = a.length; i < j; i++) { // Do something with a[i] } 53 53
54. Slide 54: Even better iteration for (var i = 0, item; item = a[i]; i++) { // Do something with item } • This trick only works with arrays that are known not to contain falsy values. The following array will break with the above idiom: var a = [10, \"dog\", false, \"elephant\"]; • (Yes, you can have mixed content in arrays) 54 54
55. Slide 55: Array methods a.toString(), a.toLocaleString(), a.concat(item, ..), a.join(sep), a.pop(), a.push(item, ..), a.reverse(), a.shift(), a.slice(start, end), a.sort(cmpfn), a.splice(start, delcount, [item]..), a.unshift([item]..) 55 55
56. Slide 56: 3.2 2.4 1.6 0.8 .8 -4 -3.2 -2.4 -1.6 -0.8 0 0.8 1.6 2.4 3.2 4 4.8 -0.8 Functions -1.6 -2.4 -3.2 56 56
57. Slide 57: Functions • Don't get much simpler than this: function add(x, y) { var total = x + y; return total; } • If nothing is explicitly returned, return value is undefined 57 57
58. Slide 58: Arguments • 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 • How is this behaviour useful? 58 58
59. Slide 59: arguments • 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 59 59
60. Slide 60: avg() • More useful: an averaging function: function avg() { var sum = 0; for (var i = 0, j = arguments.length; i < j; i++) { sum += arguments[i]; } return sum / arguments.length; } 60 60
61. Slide 61: Averaging an array? • Our fancy multi-argument function isn't much good if our data is already in an array. Do we have to rewrite it? function avgArray(arr) { var sum = 0; for (var i = 0, j = arr.length; i < j; i++) { sum += arguments[i]; } return sum / arr.length; } 61 61
62. Slide 62: Using avg() with an array • That's not necessary: > avg.apply(null, [2, 3, 4, 5]) 3.5 • Functions are objects with methods too! • The apply method takes an array of argments as the second argument... • We'll find out about the first argument a little later 62 62
63. Slide 63: Anonymous functions • The following is semantically equivalent to our earlier avg() function: var avg = function() { var sum = 0; for (var i = 0, j = arguments.length; i < j; i++) { sum += arguments[i]; } return sum / arguments.length; } 63 63
64. Slide 64: The block scope trick • Block scope is a feature of C where every set of braces defines a new scope. It can be simulated in JavaScript: var a = 1; var b = 2; (function() { var b = 3; a += b; })(); >a 4 >b 2 64 64
65. Slide 65: Recursive functions function countChars(elm) { if (elm.nodeType == 3) { // TEXT_NODE return elm.nodeValue.length; } var count = 0; for (var i = 0, child; child = elm.childNodes[i]; i++) { count += countChars(child); } return count; } 65 65
66. Slide 66: arguments.callee • arguments.callee is the current function: var charsInBody = (function(elm) { if (elm.nodeType == 3) { // TEXT_NODE return elm.nodeValue.length; } var count = 0; for (var i = 0, child; child = elm.childNodes[i]; i++) { count += arguments.callee(child); } return count; })(document.body); 66 66
67. Slide 67: arguments.callee to save state • This function remembers how many times it has been called: function counter() { if (!arguments.callee.count) { arguments.callee.count = 0; } return arguments.callee.count++; } > counter() 0 > counter() 1 67 67
68. Slide 68: http://www.flickr.com/photos/45339031@N00/100472474/ - piccadillywilson / Matt Constructors 68 68
69. Slide 69: Functions and objects function makePerson(first, last) { return { first: first, last: last } } function personFullName(person) { return person.first + ' ' + person.last; } function personFullNameReversed(person) { return person.last + ', ' + person.first } 69 69
70. Slide 70: Functions and objects (II) > s = makePerson(\"Simon\", \"Willison\"); > personFullName(s) Simon Willison > personFullNameReversed(s) Willison, Simon • Surely we can attach functions to the objects themselves? 70 70
71. Slide 71: Methods, first try function makePerson(first, last) { return { first: first, last: last, fullName: function() { return this.first + ' ' + this.last; }, fullNameReversed: function() { return this.last + ', ' + this.first; } } } 71 71
72. Slide 72: Using methods > s = makePerson(\"Simon\", \"Willison\") > s.fullName() Simon Willison > s.fullNameReversed() Willison, Simon 72 72
73. Slide 73: dot notation is required > s = makePerson(\"Simon\", \"Willison\") > var fullName = s.fullName; > fullName() undefined undefined • If you call a function without using dot notation, 'this' is set to the global object. In the browser, this is the same as 'window'. 73 73
74. Slide 74: Constructors function Person(first, last) { this.first = first; this.last = last; this.fullName = function() { return this.first + ' ' + this.last; } this.fullNameReversed = function() { return this.last + ', ' + this.first; } } var s = new Person(\"Simon\", \"Willison\"); 74 74
75. Slide 75: new • 'new' creates a new empty object and calls the specified function with 'this' set to that object. • These constructor functions should be Capitalised, as a reminder that they are designed to be called using 'new' • This is key to understanding JavaScript's object model 75 75
76. Slide 76: Sharing methods function personFullName() { return this.first + ' ' + this.last; } function personFullNameReversed() { return this.last + ', ' + this.first; } function Person(first, last) { this.first = first; this.last = last; this.fullName = personFullName; this.fullNameReversed = personFullNameReversed; } 76 76
77. Slide 77: Person.prototype function Person(first, last) { this.first = first; this.last = last; } Person.prototype.fullName = function() { return this.first + ' ' + this.last; } Person.prototype.fullNameReversed = function() { return this.last + ', ' + this.first; } 77 77
78. Slide 78: instanceof • The instanceof operator can be used to test the type of an object, based on its constructor (and prototype hierarchy, explained in the next section). var a = [1, 2, 3]; a instanceof Array true a instanceof Object true a instanceof String false 78 78
79. Slide 79: http://www.flickr.com/photos/bingolittle/5803243/ - Bingo Little Inheritance 79 79
80. Slide 80: Adding to an existing set of objects > s = new Person(\"Simon\", \"Willison\"); > s.firstNameCaps(); TypeError on line 1: s.firstNameCaps is not a function > Person.prototype.firstNameCaps = function() { return this.first.toUpperCase() } > s.firstNameCaps() SIMON 80 80
81. Slide 81: Extending core objects > var s = \"Simon\"; > s.reversed() TypeError: s.reversed is not a function > String.prototype.reversed = function() { var r = ''; for (var i = this.length - 1; i >= 0; i--){ r += this[i]; } return r; } > s.reversed() nomiS > \"This can now be reversed\".reversed() desrever eb won nac sihT 81 81
82. Slide 82: Object.prototype • All prototype chains terminate at Object.prototype • Its methods include toString(), which we can over-ride: > var s = new Person(\"Simon\", \"Willison\"); >s [object Object] > Person.prototype.toString = function() { return '<Person: ' + this.fullName() + '>'; } >s <Person: Simon Willison> 82 82
83. Slide 83: Perils of modifying Object.prototype • Remember for (var attr in obj)? • It will include stuff that's been newly added to Object.prototype • This stupid behaviour is sadly baked in to the language • Some libraries (Prototype is a prime offender) do it anyway 83 83
84. Slide 84: So what about inheritance? • Problem: JavaScript is a prototype-based language, but it pretends to be a class-based language • As a result, it doesn't do either very well • Inheritance doesn't quite behave how you would expect 84 84
85. Slide 85: Here's a special kind of person function Geek() { Person.apply(this, arguments); this.geekLevel = 5; } Geek.prototype = new Person(); Geek.prototype.setLevel = function(lvl) { this.geekLevel = lvl; } Geek.prototype.getLevel = function() { return this.geekLevel; } > s = new Geek(\"Simon\", \"Willison\") > s.fullName() Simon Willison > s.getLevel() 5 85 85
86. Slide 86: new Person()? • We're using an instance of the Person object as our prototype • We have to do this, because we need to be able to modify our prototype to add new methods that are only available to Geek instances • This is counter-intuitive and, well, a bit dumb 86 86
87. Slide 87: Solutions? • Design classes with inheritance in mind - don't do anything important in the constructor (that might break if you create an empty instance for use as a prototype) • Use one of the many workarounds – Prototype's Class.create() – The stuff you get by searching for \"javascript inheritance\" on the Web 87 87
88. Slide 88: http://en.wikipedia.org/wiki/Image:Torres_Petronas_Mayo_2004.jpg Ángel Riesgo Martínez Higher order functions 88 88
89. Slide 89: Functions are first-class objects • In English... – A function is just another object – You can store it in a variable – You can pass it to another function – You can return it from a function 89 89
90. Slide 90: VAT VAT is England's national sales tax - 17.5% var prices = [10, 8, 9.50]; var pricesVat = []; for (var i = 0; i < prices.length; i++) { pricesVat[i] = prices[i] * 1.175; } 90 90
91. Slide 91: arrayMap function arrayMap(array, func) { var result = []; for (var i = 0; i < array.length; i++) { result[i] = func(array[i]); } return result; } function calcVat(price) { return price * 1.175; } var prices = [10, 8, 9.50]; pricesVat = arrayMap(prices, calcVat); 91 91
92. Slide 92: salesTaxFactory What if we want to calculate sales tax at 4%? function salesTaxFactory(percent) { function func(price) { return price + (percent / 100) * price; } return func; } calcVat = salesTaxFactory(17.5); calc4 = salesTaxFactory(4); pricesVat = arrayMap(prices, calcVat); prices4 = arrayMay(prices, calc4); 92 92
93. Slide 93: An operation factory function makeOp(op, y) { switch (op) { case '+': return function(x) { return x + y }; case '-': return function(x) { return x - y }; case '/': return function(x) { return x / y }; case '*': return function(x) { return x * y }; default: return function(x) { return x }; } } var third = makeOp('/', 3); var dbl = makeOp('*', 2); print(third(24)); print(dbl(5)); 93 93
94. Slide 94: Closures • The previous code was an example of closures in action • A closure is a function that has captured the scope in which it was defined • Actually, functions in JavaScript have a scope chain (similar to the prototype chain) 94 94
95. Slide 95: What does this do? function openLinksInNewWindows() { for (var i = 0; i < document.links.length; i++) { document.links[i].onclick = function() { window.open(document.links[i].href); return false; } } } • The onclick function is a closure which refers back to the original scope; it does NOT retain a copy of the i variable at the time the function was created. By the time the onclick function is executed, i will be the last value assigned by the loop. 95 95
96. Slide 96: http://www.flickr.com/photos/iboy_daniel/90450551/ - iboy_daniel / doug wilson Singleton 96 96
97. Slide 97: Namespace pollution • JavaScript shares a single global namespace • It’s easy to clobber other people’s functions and variables • It’s easy for other people to clobber yours • The less code affecting the global namespace the better 97 97
98. Slide 98: The singleton pattern var simon = (function() { var myVar = 5; // Private variable function init(x) { // ... can access myVar and doPrivate } function doPrivate(x) { // ... invisible to the outside world } function doSomething(x, y) { // ... can access myVar and doPrivate } return { 'init': init, 'doSomething': doSomething } })(); simon.init(x); 98 98
99. Slide 99: Singleton benefits • Singleton lets you wrap up a complex application with dozens of functions up in a single, private namespace - a closure • This lets you expose only the functions that make up your application's external interface 99 99
100. Slide 100: http://www.flickr.com/photos/lunchtimemama/97685471/ - lunchtimemama / Scott Memory leaks 100 100
101. Slide 101: Internet Explorer sucks • To understand memory leaks, you have to understand a bit about garbage collection • Stuff gets freed up automatically when it is no longer in use (both JavaScript objects and host objects, such as DOM nodes) • IE uses different garbage collectors for JS and for the DOM, and can't handle circular references between them 101 101
102. Slide 102: This leaks function leak() { var div = document.getElementById('d'); div.obj = { 'leak': div } } • Call it enough times and IE will crash 102 102
103. Slide 103: This also leaks function sneakyLeak() { var div = document.getElementById('d'); div.onclick = function() { alert(\"hi!\"); } } • Why? Spot the closure! 103 103
104. Slide 104: Difficulties • These things can be very hard to detect - especially in large, complex applications where a cycle might occur over many nodes and JavaScript objects • One solution: function noLeak() { var div = document.getElementById('d'); div.onclick = function() { alert(\"hi!\"); } div = null; } 104 104
105. Slide 105: More solutions • Most popular JavaScript libraries have systems for attaching and detaching events • Many of these can automatically free event references when the page is unloaded • Use these, but always be aware of the problem 105 105
106. Slide 106: http://www.flickr.com/photos/javic/100567276/ - javic Performance 106 106
107. Slide 107: Performance tips • De-reference complex lookups var s = document.getElementById('d').style; s.width = '100%'; s.color = 'red'; // ... s.display = 'block'; • ... especially inside loops var lookup = foo.bar.bav; for (var i = 0; i < 1000; i++) { lookup.counter += someCalc(); } 107 107
108. Slide 108: http://www.flickr.com/photos/klara/94704029/ - klara(!) / klara Libraries 108 108
109. Slide 109: Suggested libraries ¯¯ dojotoolkit.org developer.yahoo.net/yui/ prototype.conio.net mochikit.com script.aculo.us 109 109
110. Slide 110: Tell Alex I told you this... • Everything in JavaScript is an Object. Even functions • Every object is always mutable • The dot operator is equivalent to de-referencing by hash (e.g., foo.bar === foo[\"bar\"]) • The new keyword creates an object that class constructors run inside of, thereby imprinting them • Functions are always closures (combine w/ previous rule to create OOP) • The this keyword is relative to the execution context, not the declaration context • The prototype property is mutable 110 110
111. Slide 111: http://www.flickr.com/photos/nataliedowne/14517351/ - NatBat / Natalie Downe Thank you! 111 111