Publish an object API
A module should expose several named functions or values through one CommonJS import.
Node.js · Pipe
module.exports
module.exports defines the value a CommonJS module exposes to callers. Assign an object, function, or other value to it, and require() receives that value.
How it works
module.exports is the CommonJS module value exposed to consumers. Assign an object, function, or other value to it; a later require() receives that assigned value.
Syntax
module.exports = value;Returns
The value assigned to module.exports; this is the value returned to a consumer by require().
Key points
- Use
module.exportsto choose the public value that CommonJS consumers receive fromrequire(). - The exported root can be a function, object, or another value suitable for the module's API.
- Node creates the initial export object as part of its CommonJS module machinery.
- Within a module,
exportsprovides a shorter reference to the currentmodule.exportsvalue. - The initial
exportsbinding is established before the module code runs.
Common mistakes
exportsinitially refers to the same value, but reassigningexportsalone does not replacemodule.exports.- Replacing the export changes the module's root value; add properties instead when consumers should receive an object with multiple named members.
Example: Export an object from a CommonJS module
// math.js
module.exports = {
add(a, b) {
return a + b;
}
};
// app.js
const math = require('./math.js');
console.log(math.add(2, 3));Assigning an object makes its properties available to code that loads the CommonJS module with require().
When to use it
Export a callable function
A module should be called directly after it is loaded.
Define a module boundary
A package needs one deliberate public surface while keeping implementation details module-local.
Interview questions
QWhat is module.exports used for?
module.exports defines the value a CommonJS module makes available through require(). It can be assigned an object, function, or another value.
Follow-up: What does exports mean? It is initially a shorter reference to module.exports; assigning a new value to exports does not update the module's exported value.
QHow do you export an object from CommonJS?
A module can export an object by assigning that object to module.exports. The importing code receives the object returned by require().
Follow-up: How would you export a callable module with helper properties? Assign the main function to module.exports, then add properties to that function before consumers require it.
QWhat does require() receive from a CommonJS module?
Node evaluates each file as a separate module, and module.exports is the value exposed from that module. require() returns that exported value to the caller.
Follow-up: Why can module-local variables remain private? The module system evaluates the file in its own module scope, so only values attached to the exported value are exposed.
Related
exportsrequire()modulemodule.require()Modules: CommonJS modules