book

JavaScript Enlightenment

Name: JavaScript Enlightenment
Author: Cody Lindley
ISBN: 9781449342883

by Cody Lindley

December 2012

Beginner

164 pages

3h 15m

English

O'Reilly Media, Inc.

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Preface
IntroductionWhy Did I Write This Book?Who Should Read This Book?Why JavaScript 1.5 and ECMAScript 3 Edition?Why Didn’t I Cover the Date(), Error(), and RegEx() Objects?More Code, Fewer WordsExhaustive Code and RepetitionColor-Coding ConventionsjsFiddle, JS Bin, and Firebug lite-devConventions Used in This BookUsing Code ExamplesSafari® Books OnlineHow to Contact UsAbout the AuthorAbout the Technical EditorsMichael RichardsonKyle SimpsonNathan SmithBen NadelRyan FlorenceNathan Logan
1. JavaScript Objects
Creating ObjectsJavaScript Constructors Construct and Return Object InstancesThe JavaScript Native/Built-In Object ConstructorsUser-Defined/Non-Native Object Constructor FunctionsInstantiating Constructors Using the new OperatorCreating Shorthand/Literal Values from ConstructorsPrimitive (a.k.a. Simple) ValuesThe Primitive Values null, undefined, “string”, 10, true, and false Are Not ObjectsHow Primitive Values Are Stored/Copied in JavaScriptPrimitive Values Are Equal by ValueThe String, Number, and Boolean Primitive Values Act Like Objects When Used Like ObjectsComplex (a.k.a. Composite) ValuesHow Complex Values Are Stored/Copied in JavaScriptComplex Objects Are Equal by ReferenceComplex Objects Have Dynamic PropertiesThe typeof Operator Used on Primitive and Complex ValuesDynamic Properties Allow for Mutable ObjectsAll Constructor Instances Have Constructor Properties that Point to Their Constructor FunctionVerify that an Object Is an Instance of a Particular Constructor FunctionAn Instance Created From a Constructor Can Have Its Own Independent Properties (Instance Properties)The Semantics of “JavaScript Objects” and “Object() Objects”
2. Working with Objects and Properties
Complex Objects Can Contain Most of the JavaScript Values as PropertiesEncapsulating Complex Objects in a Programmatically Beneficial WayGetting/Setting/Updating an Object’s Properties Using Dot Notation or Bracket NotationDeleting Object PropertiesHow References to Object Properties Are ResolvedUsing hasOwnProperty, Verify That an Object Property Is Not From the Prototype ChainChecking If an Object Contains a Given Property Using the in OperatorEnumerate (Loop Over) an Object’s Properties using the for in LoopHost Objects versus Native ObjectsEnhancing and Extending Objects with Underscore.js
3. Object()
Conceptual Overview of Using Object() ObjectsObject() ParametersObject() Properties and MethodsObject() Object Instance Properties and MethodsCreating Object() Objects Using “Object Literals”All Objects Inherit From Object.prototype
4. Function()
Conceptual Overview of Using Function() ObjectsFunction() ParametersFunction() Properties and MethodsFunction Object Instance Properties and MethodsFunctions Always Return a ValueFunctions Are First-Class Citizens (Not Just Syntax but Values)Passing Parameters to a Functionthis and arguments Values Available To All FunctionsThe arguments.callee PropertyThe Function Instance length Property and arguments.lengthRedefining Function ParametersReturn a Function Before It Is Done (Cancel Function Execution)Defining a Function (Statement, Expression, or Constructor)Invoking a Function [Function, Method, Constructor, or call() and apply()]Anonymous FunctionsSelf-Invoking Function ExpressionSelf-Invoking Anonymous Function StatementsFunctions Can Be NestedPassing Functions to Functions and Returning Functions from FunctionsInvoking Function Statements Before They Are Defined (Function Hoisting)A Function Can Call Itself (Recursion)
5. The Head/Global Object
Conceptual Overview of the Head ObjectGlobal Functions Contained Within the Head ObjectThe Head Object versus Global Properties and Global VariablesReferring to the Head ObjectThe Head Object Is Implied and Typically Not Referenced Explicitly
6. The this Keyword
Conceptual Overview of this and How It Refers to ObjectsHow Is the Value of this Determined?The this Keyword Refers to the Head Object in Nested FunctionsWorking Around the Nested Function Issue by Leveraging the Scope ChainControlling the Value of this Using call() or apply()Using the this Keyword Inside a User-Defined Constructor FunctionThe this Keyword Inside a Prototype Method Refers to a Constructor Instance
7. Scope and Closures
Conceptual Overview of JavaScript ScopeJavaScript Does Not Have Block ScopeUse var Inside Functions to Declare Variables and Avoid Scope GotchasThe Scope Chain (Lexical Scoping)The Scope Chain Lookup Returns the First Found ValueScope Is Determined During Function Definition, not InvocationClosures Are Caused by the Scope Chain
8. Function Prototype Property
Conceptual Overview of the Prototype ChainWhy Care About the prototype Property?Prototype Is Standard on All function() InstancesThe Default prototype Property Is an Object() ObjectInstances Created From a Constructor Function are Linked to the Constructor’s prototype PropertyLast Stop in the prototype Chain is Object.prototypeThe prototype Chain Returns the First Property Match It Finds in the ChainReplacing the prototype Property with a New Object Removes the Default Constructor PropertyInstances That Inherit Properties from the Prototype Will Always Get the Latest ValuesReplacing the prototype Property with a New Object Does Not Update Former InstancesUser-Defined Constructors Can Leverage the Same Prototype Inheritance as Native ConstructorsCreating Inheritance Chains (the Original Intention)
9. Array()
Conceptual Overview of Using Array() ObjectsArray() ParametersArray() Properties and MethodsArray Object Instance Properties and MethodsCreating ArraysAdding and Updating Values in ArraysLength versus IndexDefining Arrays with a Predefined LengthSetting Array Length can Add or Remove ValuesArrays Containing Other Arrays (Multidimensional Arrays)Looping Over an Array, Backwards and Forwards

10. String()
Conceptual Overview of Using the String() ObjectString() ParametersString() Properties and MethodsString Object Instance Properties and Methods
11. Number()
Conceptual Overview of Using the Number() ObjectIntegers and Floating-Point NumbersNumber() ParametersNumber() PropertiesNumber Object Instance Properties and Methods
12. Boolean()
Conceptual Overview of Using the Boolean() ObjectBoolean() ParametersBoolean() Properties and MethodsBoolean Object Instance Properties and MethodsNon-Primitive False Boolean Objects Convert to trueCertain Things Are false, Everything Else Is true
13. Working with Primitive String, Number, and Boolean Values
Primitive/Literal Values Are Converted to Objects When Properties Are AccessedYou Should Typically Use Primitive String, Number, and Boolean Values
14. Null
Conceptual Overview of Using the null Valuetypeof Returns null Values as “object”
15. Undefined
Conceptual Overview of the undefined ValueJavaScript ECMAScript 3 Edition (and Later) Declares the undefined Variable in the Global Scope
16. Math Function
Conceptual Overview of the Built-In Math ObjectMath Properties and MethodsMath Is Not a Constructor FunctionMath Has Constants You Cannot Augment/Mutate
A. Review
B. Conclusion
Index
About the Author
Colophon
Copyright

Content preview from JavaScript Enlightenment

Chapter 9. Array()

Conceptual Overview of Using Array() Objects

An array is an ordered list of values, typically created with the intention of looping through numerically indexed values, beginning with the index zero. What you need to know is that arrays are numerically ordered sets, versus objects, which have property names associated with values in non-numeric order. Essentially, arrays use numbers as a lookup key, while objects have user-defined property names. JavaScript does not have true associative arrays, but objects can be used to achieve the functionality of associate arrays.

Below, I store four strings in myArray that I can access using a numeric index. I compare and contrast it to an object-literal mimicking an associative array.

Live Code

<!DOCTYPE html><html lang="en"><body><script>

var myArray = ['blue', 'green', 'orange', 'red'];

console.log(myArray[0]); // logs blue using 0 index to access string in myArray

// versus

var myObject = { // a.k.a. associative array/hash, known as an object in JavaScript
   'blue': 'blue',
   'green': 'green',
   'orange': 'orange',
   'red': 'red'
};

console.log(myObject['blue']); // logs blue

</script></body></html>

Notes

Arrays can hold any type of values, and these values can be updated or deleted at any time.
If you need a “hash” (a.k.a. associative array), an object is the closest solution.
An Array() is just a special type of Object(). That is, Array() instances are basically Object() instances with a couple of extra functions (e.g., .length and ...

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JavaScript Enlightenment

by Cody Lindley

Chapter 9. Array()