The JavaScript Programming Language

 JavaScript is a stripped down version of Java  JavaScript does not exist outside browsers  JavaScript is inconsistent and buggy  JavaScript is not object-orientated

 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

 Semicolon insertion  typeof and instanceof  with and eval  == and !=  new

 Loose Typing  Dynamic Objects  Object / Array Literals  Functions / Lambdas

 Self  prototypal inheritance  dynamic objects  Scheme  lambda  loose typing  Java  syntax  conventions  Perl  regular expressions

 Numbers  Strings  Booleans  Objects  Functions

 Number  String  Boolean  Object  Function  Array  Date  RegExp  Null  Undefined

 Only one number type  No integers  64-bit floating point IEEE-754 (aka “Double”)  Numbers are Objects

(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

a = 0.1; b = 0.2; c = 0.3; (a + b) + c === a + (b + c) > false

 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

 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

> "hello".charAt(0) h > "hello, world".replace("hello", "goodbye") goodbye, world > "hello".toUpperCase() HELLO

 null = deliberately no value  undefined = no value assigned yet  Variables declared but not initialized  Object/array members that don't exist

 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 !

 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

var obj = new Object(); Or var obj = {}; These are semantically equivalent; the second is called object literal syntax and is more convenient.

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)

var obj = { name: "Carrot", "for": "Max", details: { color: "orange", size: 12 } } > obj.details.color Orange > obj["details"]["size"] 12

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

 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”

More convenient notation: > var a = ["dog", "cat", "hen"]; > a.length 3 var a = [10, "dog", false, "elephant"]; (you can have mixed content in arrays)

> 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;

 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.

 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

var a; //... function F() { var b; //... function N() { var c; //... }; }

 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

 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

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

$('#some-id').click(function(evt) { // do something on click event };

var add = function(x) { return function(y) { return x + y; }; };

function Person(name) { this.name = name; this.getName = function() { return this.name; }; } var person = new Person("some one"); person.getName(); > some one

The JavaScript Programming Language

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The JavaScript Programming Language