关于javascript模块和命名空间(Module and namespace)

我们做个项目想作为一个Module，要让它能在各个地方运行，就需要避免定义全局变量global variables和全局函数global function. 所以就要给自己的所有的variables和functions变成一个empty object 的属性或者方法，如例：

// Create an empty object as our namespace// This single global symbol will hold all of our other symbolsvar Module;if(Module && (typeof Module != "object" || Module.Name))throw new Error("Namespace 'Module' already exists");Module = {};// Define all variables and functions within the namespaceModule.max = 10;Module.define = function(){ /* code goes here*/}Module.provides = function(o, c){ /*code goes here*/}Module.sayHi = function(){ /* code goes here*/}

这样需要用的时候我们原来比如写 sayHi()， 现在这样写Module.sayHi();

另外现在更流行的一种是通过闭包作为私有命名空间和作用域，使用闭包来创建一个私有命名空间，然后将其共有方法导出到一个公有的命名空间中。

如例：

// Create the namespace object. Error checking omitted here brevity// Instead of using com.davidflanagan.Class// we can also simply say var Module={} as the example above// the reason to use com.davidflanagan.Class is just 100% ensure the name is UNIQUEvar com;if(!com) com = {};if(!com.davidflanagan) com.davidflanagan = {};com.davidflanagan.Class = {};// Don't 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 Module object// Note that we use an unnamed function so we don't create any other global symbols(function(){ // Begin anonymous function definition// Nested functions create symbols within the closurefunction define(data) {counter+=data; /* more code here*/}function provides(o, c) { /* code here*/}// local variable are symbols within the closure// This one will remain private within the closurevar counter = 0;function localMethod(){ return "This is local method"};console.log(localMethod()); // This is local method// This function can refer to the variable with a simple name// instead of having to qualify it with a namespacefunction getCounter(){ return counter;}// Now that we will 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;// Define all variables and functions within the namespacens.define = define;ns.provides = provides;ns.getCounter = getCounter;})(); // End anonymours function definition and invoke itcom.davidflanagan.Class.define(5);console.log(com.davidflanagan.Class.getCounter()); // 5console.log(com.davidflanagan.Class.localMethod()); // ERROR 命名空间中private function未经export不能被使用

更多详细内容见《犀牛书》第十章