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nodejs 如何在两个模块中共享一个对象

nodejs 如何在两个模块中共享一个对象

今天遇到一个问题,可题简单抽象为如下需求:

  • file1.js中定义了一个变量a
  • file2.js需要用到file1.js中的这个变量
  • a变量在file1.js与file2.js中均可能被加工

  • 不论在file1.js或是file2.js中,当需要获得a的值时,都需要保证获得的a值为一致的最新值,即a被file1.js或file2.js最后一次加工过的值.

    尝试

    /file1.js:

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    var foo = 0;
    var increase=function (){
    	foo += 100,
    	console.log("Value of foo in file1.js:  "+foo);
    }
    setTimeout(increase,1000);//1s后改变foo

    module.exports=foo;

    /file2.js:

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    var foo = require('./file1');

    var shout=function(){
    	console.log("Value of foo in file2.js:  "+foo);
    }
    shout();//0s时输出foo
    setTimeout(shout,2000);//2s时输出foo

运行:

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>node file2.js

输出:

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Value of foo in file2.js:  0
file1 has increased the foo to:  100
Value of foo in file2.js:  0

file1在修改foo为100后,file2再次读取仍为0

修改代码

/file1.js:

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var foo = ["0"];

var shout=function(){
	console.log("Value of foo in file1.js:  "+foo);
}
var increase=function (){
	foo .push("100"),
	console.log("file1 has increased the foo to:  "+foo);
}
shout();
setTimeout(increase,1000);//1s后改变a值
setTimeout(shout,2000);
setTimeout(shout,4000);

module.exports=foo;

/file2.js:

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var foo = require('./file1');

var shout=function(){
	console.log("Value of foo in file2.js:  "+foo);
}
var increase=function (){
	foo .push("100"),
	console.log("file2 has change the foo to:  "+foo);
}
shout();
setTimeout(shout,2000);
setTimeout(increase,3000);//
setTimeout(shout,4000);

运行:

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>node file2.js

输出:

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Value of foo in file1.js:  0
Value of foo in file2.js:  0
file1 has increased the foo to:  0,100
Value of foo in file1.js:  0,100
Value of foo in file2.js:  0,100
file2 has change the foo to:  0,100,100
Value of foo in file1.js:  0,100,100
Value of foo in file2.js:  0,100,100

当exports暴露出的变量类型为number或string时,会拷贝一个副本给引用者,而exports一个list或dict,则会将该list或dict的实例地址暴露路给引用者,要想将number或string也作为共享变量,可以将number或string放入list或map来实现.

示例

/file1.js:

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var foo = {a:0};

var shout=function(){
	console.log("Value of foo in file1.js:  "+foo.a);
}
var increase=function (){
	foo.a += 1,
	console.log("file1 has increased the foo to:  "+foo.a);
}
shout();
setTimeout(increase,1000);//1s后改变a值
setTimeout(shout,2000);
setTimeout(shout,4000);

module.exports=foo;

/file2.js:

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var foo = require('./file1');

var shout=function(){
	console.log("Value of foo in file2.js:  "+foo.a);
}
var increase=function (){
	foo.a += 1,
	console.log("file2 has change the foo to:  "+foo.a);
}
shout();
setTimeout(shout,2000);
setTimeout(increase,3000);//
setTimeout(shout,4000);

运行:

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>node file2.js

输出:

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Value of foo in file1.js:  0
Value of foo in file2.js:  0
file1 has increased the foo to:  1
Value of foo in file1.js:  1
Value of foo in file2.js:  1
file2 has change the foo to:  2
Value of foo in file1.js:  2
Value of foo in file2.js:  2

这样,就可以在两个模块中共享同一对象