JavaScript_Succinctly

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een defined. You might think that because myArray.foo is not a property of the myArray object, JavaScript will immediately return undefined. But JavaScript will look in two more places (Array.prototype and then Object.prototype) for the value of foo before it returns undefined. Sample: sample37.html var myArray = []; console.log(myArray.foo); // Logs undefined. /* JS will look at Array.prototype for Array.prototype.foo, but it is not there. Then it will look for it at Object.prototype, but it is not there either, so undefined is returned! */ When I attempt to access a property of an object, it will check that object instance for the property. If it has the property, it will return the value of the property, and there is no inheritance occurring because the prototype chain is not leveraged. If the instance does not have the property, JavaScript will then look for it on the object's constructor function prototype object. All object instances have a property that is a secret link (aka __proto__) to the constructor function that created the instance. This secret link can be leveraged to grab the constructor function, specifically the prototype property of the instance’s constructor function. This is one of the most confusing aspects of objects in JavaScript. But let's reason this out. Remember that a function is also an object with properties. It makes sense to allow objects to inherit properties from other objects. Just like saying: "Hey object B, I would like you to share all the properties that object A has." JavaScript wires this all up for native objects by default via the prototype object. When you create your own constructor functions, you can leverage prototype chaining as well. How exactly JavaScript accomplishes this is confusing until you see it for what it is: just a set of rules. Let's create an array to examine the prototype property closer. Sample: sample38.html // myArray is an Array object. var myArray = ['foo', 'bar']; 52
console.log(myArray.join()); // join() is actually defined at Array.prototype.join Our Array() instance is an object with properties and methods. As we access one of the array methods, such as join(), let’s ask ourselves: Does the myArray instance created from the Array() constructor have its own join() method? Let's check. Sample: sample39.html var myArray = ['foo', 'bar']; console.log(myArray.hasOwnProperty('join')); // Logs false. No it does not. Yet myArray has access to the join() method as if it were its own property. What happened here? Well, you just observed the prototype chain in action. We accessed a property that, although not contained in the myArray object, could be found by JavaScript somewhere else. That somewhere else is very specific. When the Array() constructor was created by JavaScript, the join() method was added (among others) as a property of the prototype property of Array(). To reiterate, if you try to access a property on an object that does not contain it, JavaScript will search the prototype chain for this value. First it will look at the constructor function that created the object (e.g., Array), and inspect its prototype (e.g., Array.prototype) to see if the property can be found there. If the first prototype object does not have the property, then JavaScript keeps searching up the chain at the constructor behind the initial constructor. It can do this all the way up to the end of the chain. Where does the chain end? Let's examine the example again, invoking the toLocaleString() method on myArray. Sample: sample40.html // myArray and Array.prototype contain no toLocaleString() method. var myArray = ['foo', 'bar']; // toLocaleString() is actually defined at Object.prototype.toLocaleString 53
Page 2 and 3: By Cody Lindley Foreword by Daniel
Page 4 and 5: Table of Contents About the Author
Page 6 and 7: Object() object instance properties
Page 8 and 9: The Story behind the Succinctly Ser
Page 10 and 11: About the Author Cody Lindley is a
Page 12 and 13: Advanced technical books written ab
Page 14 and 15: “Consider that the cody object cr
Page 16 and 17: Chapter 1 JavaScript Objects Creati
Page 18 and 19: Using JavaScript, the getGender met
Page 20 and 21: * The String() constructor function
Page 22 and 23: new object that is returned from th
Page 24 and 25: Notes The Math object is the oddbal
Page 26 and 27: In this snippet, we created a new s
Page 28 and 29: Verify that literals are created fr
Page 30 and 31: The primitive values null, undefine
Page 32 and 33: The concept to take away here is th
Page 34 and 35: * This will throw an error and not
Page 36 and 37: copied, but not the actual value. T
Page 38 and 39: Sample: sample21.html // Primitive
Page 40 and 41: Notes Careful! If you mutate the na
Page 42 and 43: console.log(instanceOfCustomObject.
Page 44 and 45: myObject.prop = 'test'; myArray.pro
Page 46 and 47: Chapter 2 Working with Objects and
Page 48 and 49: Sample: sample31.html // Encapsula
Page 50 and 51: cody['getGender']() // Just slap th
Page 54 and 55: console.log(myArray.toLocaleString(
Page 56 and 57: Sample: sample44.html var cody = {
Page 58 and 59: Sometimes a web browser manufacture
Page 60 and 61: I like this library because it take
Page 62 and 63: console.log(stringObject); // Logs
Page 64 and 65: Chapter 4 Number() Conceptual overv
Page 66 and 67: NEGATIVE_INFINITY POSITIVE_INFINIT
Page 68 and 69: Parameter passed to Boolean() = Mat
Page 70 and 71: console.log(Boolean(Math)); console
Page 72 and 73: var numberObject = new Number(1.100
Page 74 and 75: Chapter 7 Null Conceptual overview
Page 76 and 77: Chapter 8 Undefined Conceptual over
Page 78 and 79: Chapter 9 The Head/Global Object Co
Page 80 and 81: object. } // Logs bar, foo's value
Page 82 and 83: Make sure you understand that the h
Page 84 and 85: Object() parameters The Object() co
Page 86 and 87: Sample: sample72.html var cody = n
Page 88 and 89: Logs 'foo', being found at Object.p
Page 90 and 91: Sample: sample77.html var addFunct
Page 92 and 93: Sample: sample79.html var yelp = f
Page 94 and 95: parameters when defining the functi
Page 96 and 97: Notes The arguments.length property
Page 98 and 99: Invoking a function (function, meth
Page 100 and 101: Self-invoking anonymous function st
Page 102 and 103:
the bar variable. All this is to sh
Page 104 and 105:
Chapter 12 The this Keyword Concept
Page 106 and 107:
Clearly, the value of this is based
Page 108 and 109:
Working around the nested function
Page 110 and 111:
What you need to learn here is that
Page 112 and 113:
var john = new Person(); // No argu
Page 114 and 115:
Notes An unlimited number of functi
Page 116 and 117:
} (); How is the value of sayHiTex
Page 118 and 119:
var parentFunction = function () {
Page 120 and 121:
Chapter 14 Function Prototype Prope
Page 122 and 123:
Sample: sample119.html var myFunct
Page 124 and 125:
In this example, the foo property i
Page 126 and 127:
console.log(FooInstance.constructor
Page 128 and 129:
Providing a new object as the proto
Page 130 and 131:
var chuck = new Person(0, 0); conso
Page 132 and 133:
An Array() is just a special type o
Page 134 and 135:
It is more common to see an array d
Page 136 and 137:
console.log(myArray.length); // Log
Page 138 and 139:
while (myArrayLength--) { // If len
Page 140 and 141:
ceil() cos() exp() floor() log() ma
Page 142 and 143:
That is: a complex value is equal t
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JavaScript_Succinctly

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