javascript node.js 中的模块如何维护状态？
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How can a module in node.js maintain state?
提问by foreyez
I have two different js files that use the same module.
我有两个使用相同模块的不同 js 文件。
file1.js:
文件1.js：
var mod1 = require('commonmodule.js');
mod1.init('one');
file2.js:
file2.js：
var mod2 = require('commonmodule.js');
mod2.init('two');
(both these files file1.js, file2.js are loaded inside my server.js file, they themselves are modules)
（这两个文件 file1.js、file2.js 都加载到我的 server.js 文件中，它们本身就是模块）
now in commonmodule.js:
现在在 commonmodule.js 中：
var savedName;
exports.init = function(name)
{
savedName = name;
}
exports.getName = function()
{
return savedName;
}
I noticed that this savedName is always overridden dependent on who set it last.So it doesn't seem to work. How would I get a module to maintain state?
我注意到这个 saveName 总是被覆盖取决于谁最后设置它。所以它似乎不起作用。我如何获得一个模块来维护状态？
Note: I also tried to set savedName as exports.savedName in the commonmodule.js but it doesn't work either
注意：我也尝试在 commonmodule.js 中将savedName 设置为exports.savedName 但它也不起作用
回答by Miguel Mota
You can just create a new instance every time the module is required:
每次需要模块时，您都可以创建一个新实例：
commonmodule.js
通用模块.js
function CommonModule() {
var savedName;
return {
init: function(name) {
savedName = name;
},
getName: function() {
return savedName;
}
};
}
module.exports = CommonModule;
file1.js
文件1.js
var mod1 = new require('./commonmodule')();
mod1.init('one');
console.log(mod1.getName()); // one
file2.js
文件2.js
var mod2 = new require('./commonmodule')()
mod2.init('two');
console.log(mod2.getName()); // two
回答by Peter Lyons
modules in and of themselves are simple object instances. A single instance will be shared by all other modules (with the caveat that it is loaded via the same path). If you want state, use a class and export a constructor function.
模块本身就是简单的对象实例。单个实例将被所有其他模块共享（注意它是通过相同路径加载的）。如果需要状态，请使用类并导出构造函数。
example:
例子：
//Person.js
function Person(name) {
this.name = name;
}
module.exports = Person;
To use it:
要使用它：
var Person = require("./Person");
var bob = new Person("Bob");
回答by JAB
Modules are not like classes/class functions; by default, mod1and mod2will refer to the same module due to caching. To keep track of per-instance state, you'll need a constructor function or something similar inside your module, e.g.
模块不像类/类函数；默认情况下，由于缓存mod1，mod2将引用相同的模块。为了跟踪每个实例的状态，你需要一个构造函数或模块内部的类似东西，例如
var mod = require('commonmodule.js');
var state = new mod.init('one');
Where initdefines the stateful object. You could also have it return an object literal, in which case you wouldn't have to use new(e.g. var state = require('commonmodule.js').init('one');)
其中init定义了有状态对象。你也可以让它返回一个对象文字，在这种情况下你不必使用new（例如var state = require('commonmodule.js').init('one');）
(This is assuming you want the module to have other, shared state in addition to the per-instance state; if that is not the case, Peter Lyons' method would be simpler.)
（这是假设除了每个实例的状态之外，您还希望模块具有其他共享状态；如果不是这种情况，Peter Lyons 的方法会更简单。）
回答by Vinz243
You could perhaps remove from cache your module. Like that:
您也许可以从缓存中删除您的模块。像那样：
file1.js:
文件1.js：
var mod1 = require('commonmodule.js');
mod1.init('one');
file2.js:
file2.js：
delete require.cache[require.resolve(modulename)];
var mod2 = require('commonmodule.js');
mod2.init('two');
But I don't find it very convenient and clean.
但我觉得它不是很方便和干净。
But you could also clone itor make a small proxy.
但是您也可以克隆它或制作一个小型代理。
Also you could create classes:
你也可以创建类：
var savedName;
exports.obj = {}
exports.obj.prototype.init = function(name)
{
savedName = name;
}
exports.obj.prototype.getName = function()
{
return savedName;
}
Then :
然后 ：
var mod2 = new (require('commonmodule.js'))();
mod2.init('two');
