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@ -27,26 +27,33 @@ The contents of `circle.js`: |
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}; |
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The module `circle.js` has exported the functions `area()` and |
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`circumference()`. To export an object, add to the special `exports` |
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object. |
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`circumference()`. To add functions and objects to the root of your module, |
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you can add them to the special `exports` object. |
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Note that `exports` is a reference to `module.exports` making it suitable |
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for augmentation only. If you are exporting a single item such as a |
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constructor you will want to use `module.exports` directly instead. |
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Variables local to the module will be private, as though the module was wrapped |
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in a function. In this example the variable `PI` is private to `circle.js`. |
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function MyConstructor (opts) { |
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//... |
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} |
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If you want the root of your module's export to be a function (such as a |
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constructor) or if you want to export a complete object in one assignment |
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instead of building it one property at a time, assign it to `module.exports` |
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instead of `exports`. |
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// BROKEN: Does not modify exports |
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exports = MyConstructor; |
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Below, `bar.js` makes use of the `square` module, which exports a constructor: |
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// exports the constructor properly |
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module.exports = MyConstructor; |
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var square = require('./square.js'); |
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var mySquare = square(2); |
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console.log('The area of my square is ' + mySquare.area()); |
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Variables |
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local to the module will be private. In this example the variable `PI` is |
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private to `circle.js`. |
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The `square` module is defined in `square.js`: |
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// assigning to exports will not modify module, must use module.exports |
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module.exports = function(width) { |
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return { |
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area: function() { |
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return width * width; |
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} |
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}; |
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} |
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The module system is implemented in the `require("module")` module. |
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@ -232,18 +239,21 @@ would resolve to different files. |
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* {Object} |
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In each module, the `module` free variable is a reference to the object |
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representing the current module. In particular |
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`module.exports` is accessible via the `exports` module-global. |
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`module` isn't actually a global but rather local to each module. |
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representing the current module. For convenience, `module.exports` is |
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also accessible via the `exports` module-global. `module` isn't actually |
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a global but rather local to each module. |
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### module.exports |
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* {Object} |
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The `module.exports` object is created by the Module system. Sometimes this is not |
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acceptable, many want their module to be an instance of some class. To do this |
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assign the desired export object to `module.exports`. For example suppose we |
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were making a module called `a.js` |
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acceptable; many want their module to be an instance of some class. To do this |
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assign the desired export object to `module.exports`. Note that assigning the |
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desired object to `exports` will simply rebind the local `exports` variable, |
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which is probably not what you want to do. |
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For example suppose we were making a module called `a.js` |
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var EventEmitter = require('events').EventEmitter; |
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@ -277,6 +287,28 @@ y.js: |
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var x = require('./x'); |
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console.log(x.a); |
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#### exports alias |
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The `exports` variable that is available within a module starts as a reference |
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to `module.exports`. As with any variable, if you assign a new value to it, it |
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is no longer bound to the previous value. |
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To illustrate the behaviour, imagine this hypothetical implementation of |
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`require()`: |
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function require(...) { |
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// ... |
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function (module, exports) { |
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// Your module code here |
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exports = some_func; // re-assigns exports, exports is no longer |
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// a shortcut, and nothing is exported. |
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module.exports = some_func; // makes your module export 0 |
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} (module, module.exports); |
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return module; |
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} |
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As a guideline, if the relationship between `exports` and `module.exports` |
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seems like magic to you, ignore `exports` and only use `module.exports`. |
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### module.require(id) |
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