簡而言之 exports是 module.exports本地文件中的快捷方式（相當(dāng)于引用）棚瘟，它不能很好的實(shí)現(xiàn)導(dǎo)出功能嗜憔。

a.js

exports.f = 123123

b.js

const a = require('./a');
console.log(a.f);

這樣可以正常從a導(dǎo)出，在b.js中引用
a.js中改為exports = {f: 123}無法導(dǎo)出
a.js中改為module.exports = {f: 123}正常導(dǎo)出

以下為官方文檔翻譯：

module.exports#

Added in: v0.1.16

• <Object>
  module.exports對(duì)象是由Module系統(tǒng)創(chuàng)建的，有時(shí)這是不能被接受的怜奖；很多人希望他們的module是一些class的實(shí)例。為此翅阵，將期望導(dǎo)出的對(duì)象賦值到module.exports歪玲。需要注意的是賦值期望的對(duì)象到exports會(huì)簡單的將本地exports變量重新綁定，這很可能并不是所期望的結(jié)果掷匠。

The module.exportsobject is created by the Module system. Sometimes this is not acceptable; many want their module to be an instance of some class. To do this, assign the desired export object to module.exports. Note that assigning the desired object to exports will simply rebind the local exports variable, which is probably not what is desired.

舉個(gè)例子滥崩，假設(shè)我們建了一個(gè)叫a.js的模塊
For example suppose we were making a module called a.js

const EventEmitter = require('events');

module.exports = new EventEmitter();

// Do some work, and after some time emit
// the 'ready' event from the module itself.
// 搞點(diǎn)事情，過一秒之后將'ready'事件從模塊自身提交出去
setTimeout(() => {
  module.exports.emit('ready');
}, 1000);

在另一個(gè)文件中我們可以這么做
Then in another file we could do

const a = require('./a');
a.on('ready', () => {
  console.log('module a is ready');
});

要注意給module.exports賦值必須立即執(zhí)行讹语，而不能在回調(diào)中進(jìn)行钙皮，以下為錯(cuò)誤示例：

Note that assignment to module.exports must be done immediately. It cannot be done in any callbacks. This does not work:

x.js:

setTimeout(() => {
  module.exports = { a: 'hello' };
}, 0);

y.js:

const x = require('./x');
console.log(x.a);

exports shortcut#

Added in: v0.1.16
exports變量在模塊的文件級(jí)范圍內(nèi)是有效的，并且會(huì)在模塊評(píng)估之前被賦值為module.exports的值

它允許有一個(gè)快捷鍵顽决，所以module.exports.f = ...可以更簡潔的寫為exports.f = ...然而短条，要意識(shí)到，和其他變量一樣才菠，假如有一個(gè)新的值被賦到exports上茸时，那么它將不再綁定到module.exports:

The exportsvariable is available within a module's file-level scope, and is assigned the value of module.exports before the module is evaluated.

It allows a shortcut, so that module.exports.f = ... can be written more succinctly as exports.f = .... However, be aware that like any variable, if a new value is assigned to exports, it is no longer bound to module.exports:

module.exports.hello = true; // Exported from require of module 從需求模塊中導(dǎo)出
exports = { hello: false };  // Not exported, only available in the module 沒有導(dǎo)出，僅在模塊中有效

當(dāng)module.exports屬性被完全替換為一個(gè)新的對(duì)象時(shí)赋访，通常也會(huì)重新賦值exports可都，例如：
When the module.exports property is being completely replaced by a new object, it is common to also reassign exports, for example:

module.exports = exports = function Constructor() {
  // ... etc.
};

為了闡明這個(gè)行為缓待，猜想一下require()的假想實(shí)現(xiàn)（比實(shí)際簡單很多）：
To illustrate the behavior, imagine this hypothetical implementation of require(), which is quite similar to what is actually done by require():

function require(/* ... */) {
  const module = { exports: {} };
  ((module, exports) => {
    // Module code here. In this example, define a function.
    function someFunc() {}
    exports = someFunc;
    // At this point, exports is no longer a shortcut to module.exports, and
    // this module will still export an empty default object.
    module.exports = someFunc;
    // At this point, the module will now export someFunc, instead of the
    // default object.
  })(module, module.exports);
  return module.exports;
}

原文鏈接