作为参数传入时，无法设置module.exports

Question

I am building my bundle using Browserify .

I have the following service.js :

(function (exports, require) {

     // ...
     var Service = function (name, region) {
         this.name = name;
         this.region = region;
         // ...
     }

     exports = Service;

})(module.exports, require);

Whenever I try to require('./service') on another module, I get an empty object as if the exports object was never set.

If I use module.exports without the argument encapsulation, everything works fine:

(function (require) {

   // ...
     var Service = function (name, region) {
         this.name = name;
         this.region = region;
         // ...
     }

     module.exports = Service;

})(require);

Why does this happen and why is this required?

Answer 1

In your first example, example is a variable scoped within your anonymous function, and it's pointing to module.exports . When you say exports = Service , you're changing what exports is pointing to, not what module.exports is pointing to.

When you say module.exports = Service , you're changing a property of module , which is globally scoped.

An additional illustration:

(function (m, require) {

    // ...
    var Service = function (name, region) {
        this.name = name;
        this.region = region;
        // ...
    }

    m.exports = Service;

})(module, require);

m points to module , and when we set m.exports , we're setting module.exports , since m and module point to the same object.