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Made some corrections and clarifications
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@ -104,9 +104,10 @@ false
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// There's also null and undefined
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null // used to indicate a deliberate non-value
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undefined // used to indicate a value that hasn't been set yet
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undefined // used to indicate a value is not currently present (although undefined
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// is actually a value itself)
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// null, undefined, NaN, 0 and "" are falsy, and everything else is truthy.
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// false, null, undefined, NaN, 0 and "" are falsy, and everything else is truthy.
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// Note that 0 is falsy and "0" is truthy, even though 0 == "0".
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///////////////////////////////////
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@ -142,7 +143,7 @@ myArray[1] // = 45
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// JavaScript's objects are equivalent to 'dictionaries' or 'maps' in other
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// languages: an unordered collection of key-value pairs.
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{key1: "Hello", key2: "World"}
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var myObj = {key1: "Hello", key2: "World"}
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// Keys are strings, but quotes aren't required if they're a valid
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// JavaScript identifier. Values can be any type.
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@ -211,9 +212,13 @@ function myFunction(thing){
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myFunction("foo") // = "FOO"
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// Functions can also be defined "anonymously" - without a name:
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function(thing){
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(function(thing){
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return thing.toLowerCase()
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}
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})
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// Note: Stand-alone function declarations require an identifier name.
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// Anonymous functions are values, not declarations, so they must be
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// treated as a value. We wrap ours here in ( ) to do so, or you could assign
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// it to a variable, or pass it as a parameter to another function.
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// (we can't call our function, since we don't have a name to refer to it with)
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// JavaScript functions are first class objects, so they can be reassigned to
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@ -247,12 +252,15 @@ i // = 5 - not undefined as you'd expect in a block-scoped language
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// in a web browser is always 'window'. The global object may have a
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// different name in non-browser environments such as Node.js.
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window.permanent = 10
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// Or, as previously mentioned, we can just leave the var keyword off.
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// Or, as previously mentioned, if you leave the var keyword off, a
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// global variable will be created when you assign it a value. However,
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// this behavior is frowned upon, and in fact is disallowed in "strict
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// mode".
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permanent2 = 15
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})()
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temporary // raises ReferenceError
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permanent // = 10
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permanent2 // = 15
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permanent2 // = 15 <-- the accidental global variable
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// One of JavaScript's most powerful features is closures. If a function is
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// defined inside another function, the inner function has access to all the
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@ -268,6 +276,12 @@ function sayHelloInFiveSeconds(name){
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// access to the value of prompt.
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}
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sayHelloInFiveSeconds("Adam") // will open a popup with "Hello, Adam!" in 5s
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// inner() has access to the variable "prompt" strictly because of lexical scope.
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// A closure is being demonstrated because the inner() function is being executed
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// at a later time, and in fact being executed "outside" the scope where it was
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// declared (inside of the implementation of setTimeout()), but yet inner() STILL
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// has access to the variable "prompt". It is said that inner() has a "closure"
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// over the variables of sayHelloInFiveSeconds().
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///////////////////////////////////
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// 5. More about Objects; Constructors and Prototypes
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