《JS学习笔记》word版.doc

JS学习笔记一：Creating Modules and Namespaces。/the first rule of JavaScript modules: a module should never add more than a single symbol to the global namespace./ Create an empty object as our namespace/ This single global symbol will hold all of our other symbolsvar Class = ;/ Define functions within the namespaceClass.define = function(data) /* code goes here */ Cvides = function(o, c) /* code goes here */ In the case of the class module, you can put the code in a file named Class.js and begin that file with a comment that looks like this:/* * Class.js: A module of utility functions for working with classes. * * This module defines a single global symbol named Class. * Class refers to a namespace object, and all utility functions * are stored as properties of this namespace. */Example 10-1. Creating a namespace based on a domain name/ Create the global symbol com if it doesnt exist/ Throw an error if it does exist but is not an objectvar com;if (!com) com = ;else if (typeof com != object) throw new Error(com already exists and is not an object);/ Repeat the creation and type-checking code for the next levelif (!com.davidflanagan) com.davidflanagan = else if (typeof com.davidflanagan != object) throw new Error(com.davidflanagan already exists and is not an object);/ Throw an error if com.davidflanagan.Class already existsif (com.davidflanagan.Class) throw new Error(com.davidflanagan.Class already exists);/ Otherwise, create and populate the namespace with one big object literalcom.davidflanagan.Class = define: function(data) /* code here */ , provides: function(o, c) /* code here */ ;var com; / Declare global symbol before testing for its presenceif (!com | !com.davidflanagan | !com.davidflanagan.Class) throw new Error(com/davidflanagan/Class.js has not been loaded);/* * com/davidflanagan/Shapes.js: a module of classes representing shapes * * This module defines classes within the com.davidflanagan.shapes namespace * This module requires the com/davidflanagan/Class.js module */ First, check for the Class modulevar com; / Declare global symbol before testing for its presenceif (!com | !com.davidflanagan | !com.davidflanagan.Class) throw new Error(com/davidflanagan/Class.js has not been loaded);/ Import a symbol from that modulevar define = com.davidflanagan.Class.define;/ We know from the test for the Class module that the com.davidflanagan/ namespace exists, so we dont have to create it here./ We just create our shapes namespace within it.if (com.davidflanagan.shapes) throw new Error(com.davidflanagan.shapes namespace already exists);/ Create the namespacecom.davidflanagan.shapes = ;/ Now define classes, storing their constructor functions in our namespacecom.davidflanagan.shapes.Circle = define( /* class data here */ );com.davidflanagan.shapes.Rectangle = define( /* class data here */ );com.davidflanagan.shapes.Triangle = define( /* class data here */);(function( ) / Define an anonymous function. No name means no global symbol / Code goes here / Any variables are safely nested within the function, / so no global symbols are created.)( ); / End the function definition and invoke it./ This is an easier name, to save typing.var define = com.davidflanagan.Class.define; ？important things to understand about importing symbols1you can import only symbols that refer to a function, object, or array。2Module developers must always use the fully qualified name of their symbols./ Create a simple namespace. No error checking required. The/ module user knows that this symbol does not exist yet.var Class = ;/ Now import a symbol into this new namespace.Class.define = com.davidflanagan.Class.define;/ A property of primitive type; cannot be importedcom.davidflanagan.Class.counter = 0;/ Here is an accessor method that can be importedcom.davidflanagan.Class.getCounter = function( ) return com.davidflanagan.Class.counter;/ Create the namespace object. Error checking omitted here for brevity.var com;if (!com) com = ;if (!com.davidflanagan) com.davidflanagan = ;com.davidflanagan.Class = ;/ Dont stick anything into the namespace directly./ Instead we define and invoke an anonymous function to create a closure/ that serves as our private namespace. This function will export its/ public symbols from the closure into the com.davidflanagan.Class object/ Note that we use an unnamed function so we dont create any other/ global symbols.(function( ) / Begin anonymous function definition / Nested functions create symbols within the closure function define(data) counter+; /* more code here */ function provides(o, c) /* code here */ / Local variable are symbols within the closure. / This one will remain private within the closure var counter = 0; / This function can refer to the variable with a simple name / instead of having to qualify it with a namespace function getCounter( ) return counter; / Now that weve defined the properties we want in our private / closure, we can export the public ones to the public namespace / and leave the private ones hidden here. var ns = com.davidflanagan.Class; ns.define = define; vides = provides; ns.getCounter = getCounter;)( ); / End anonymous function definition and invoke it/* * Module.js: module and namspace utilities * * This is a module of module-related utility functions that are * compatible with JSAN-type modules. * This module defines the namespace Module. */ Make sure we havent already been loadedvar Module;if (Module & (typeof Module != object | Module.NAME) throw new Error(Namespace Module already exists);/ Create our namespaceModule = ;/ This is some metainformation about this namespaceModule.NAME = Module; / The name of this namespaceModule.VERSION = 0.1; / The version of this namespace/ This is the list of public symbols that we export from this namespace./ These are of interest to programers who use modules.Module.EXPORT = require, importSymbols;/ These are other symbols we are willing to export. They are ones normally/ used only by module authors and are not typically imported.Module.EXPORT_OK = createNamespace, isDefined, registerInitializationFunction, runInitializationFunctions, modules, globalNamespace;/ Now start adding symbols to the namespaceModule.globalNamespace = this; / So we can always refer to the global scopeModule.modules = Module: Module ; / Module name-namespace map./* * This function creates and returns a namespace object for the * specified name and does useful error checking to ensure that the * name does not conflict with any previously loaded module. It * throws an error if the namespace already exists or if any of the * property components of the namespace exist and are not objects. * * Sets a NAME property of the new namespace to its name. * If the version argument is specified, set the VERSION property * of the namespace. * * A mapping for the new namespace is added to the Module.modules object */Module.createNamespace = function(name, version) / Check name for validity. It must exist, and must not begin or / end with a period or contain two periods in a row. if (!name) throw new Error(Module.createNamespace( ): name required); if (name.charAt(0) = . | name.charAt(name.length-1) = . | name.indexOf(.) != -1) throw new Error(Module.createNamespace( ): illegal name: + name); / Break the name at periods and create the object hierarchy we need var parts = name.split(.); / For each namespace component, either create an object or ensure that / an object by that name already exists. var container = Module.globalNamespace; for(var i = 0; i parts.length; i+) var part = partsi; / If there is no property of container with this name, create / an empty object. if (!containerpart) containerpart = ; else if (typeof containerpart != object) / If there is already a property, make sure it is an object var n = parts.slice(0,i).join(.); throw new Error(n + already exists and is not an object); container = containerpart; / The last container traversed above is the namespace we need. var namespace = container; / It is an error to define a namespace twice. It is okay if our / namespace object already exists, but it must not already have a / NAME property defined. if (namespace.NAME) throw new Error(Module +name+ is already defined); / Initialize name and version fields of the namespace namespace.NAME = name; if (version) namespace.VERSION = version; / Register this namespace in the map of all modules Module.modulesname = namespace; / Return the namespace object to the caller return namespace;/* * Test whether the module with the specified name has been defined. * Returns true if it is defined and false otherwise. */Module.isDefined = function(name) return name in Module.modules;/* * This function throws an error if the named module is not defined * or if it is defined but its version is less than the specified version. * If the namespace exists and has a suitable version, this function simply * returns without doing anything. Use this function to cause a fatal * error if the modules that your code requires are not present. */Module.require = function(name, version) if (!(name in Module.modules) throw new Error(Module + name + is not defined); / If no version was specified, there is nothing to check if (!version) return; var n = Module.modulesname; / If the defined version is less than the required version or if / the namespace does not declare any version, throw an error. if (!n.VERSION | n.VERSION 1 & typeof arguments1 = object) if (arguments1 != null) to = arguments1; firstsymbol = 2; / Now get the list of specified symbols for(var a = firstsymbol; a arguments.length; a+) symbols.push(argumentsa); / If we were not passed any symbols to import, import a set defined / by the module, or just import all of them. if (symbols.length = 0) / If the module defines an EXPORT array, import / the symbols in that array. if (from.EXPORT) for(var i = 0; i from.EXPORT.length; i+) var s = from.EXPORTi; tos = froms; return; / Otherwise if the modules does not define an EXPORT_OK array, / just import everything in the modules namespace else if (!from.EXPORT_OK) for(s in from) tos = froms; return; / If we get here, we have an explicitly specified array of symbols / to import. If the namespace defines EXPORT and/or EXPORT_OK arrays, / ensure that each symbol is listed before importing it. / Throw an error if a requested symbol does not exist or if / it is not allowed to be exported. var allowed; if (from.EXPORT | from.EXPORT_OK) allowed = ; / Copy allowed symbols from arrays to properties of an object. / This allows us to test for an allowed symbol more efficiently. if (from.EXPORT) for(var i = 0; i from.EXPORT.length; i+) allowedfrom.EXPORTi = true; if (from.EXPORT_OK) for(var i = 0; i from.EXPORT_OK.length; i+) allowedfrom.EXPORT_OKi = true; / Import the symbols for(var i = 0; i symbols.length; i+) var s = symbolsi; / The name of the symbol to import if (!(s in from) / Make sure it exists throw new Error(Module.importSymbols( ): symbol + s + is not defined); if (allowed & !(s in allowed) / Make sure it is a public symbol throw new Error(Module.importSymbols( ): symbol + s + is not public and cannot be imported.); tos = froms; / Import it ;/ Modules use this function to register one or more initialization functionsModule.registerInitializationFunction = function(f) / Store the function in the array of initialization functions Module._initfuncs.push(f); / If we have not yet registered an onload event handler, do so now. Module._registerEventHandler( );/ A function to invoke all registered initialization functions./ In client-side JavaScript, this will automatically be called in/ when the document finished loading. In other contexts, you must/ call it explicitly.Module.runInitializationFunctions = function( ) / Run each initialization function, catching and ignoring exceptions / so that a failure by one mod