module-invalidate

Invalidate node.js modules loaded through require()

Description

module-invalidate allows you to invalidate a given module (or all modules) and make it automatically reloaded on further access, no need to call require() again.

Install

npm install --save module-invalidate

Examples

Example: simple case

module ./myModule.js

module.invalidable = true;
 
var count = 0;
exports.count = function() {
 
    return count++;
}

main module ./index.js

require('module-invalidate');
 
var myModule = require('./myModule.js');
 
console.log( myModule.count() ); // 0
console.log( myModule.count() ); // 1
 
module.constructor.invalidateByExports(myModule);
 
console.log( myModule.count() ); // 0
console.log( myModule.count() ); // 1

Example: invalidate module on modification

const fs = require('fs');
 
var myModule = require('./myModule.js');
 
fs.watch(require.resolve('./myModule.js'), function() {
    
    module.invalidateByPath('./myModule.js');
});
 
setInterval(function() {
    
    console.log(myModule.count());
}, 1000);

Example:

require('module-invalidate');
 
var tmp_modulePath = require('path').join(__dirname, 'tmp_module.js');
 
require('fs').writeFileSync(tmp_modulePath, `
    module.invalidable = true;
    exports.a = 1;
`);
 
 
var tmp_module = require('./tmp_module.js');
 
console.log(tmp_module.a); // 1
 
 
require('fs').writeFileSync(tmp_modulePath, `
    module.invalidable = true;
    exports.a = 2;
`);
 
module.constructor.invalidateByExports(tmp_module);
 
console.log(tmp_module.a); // 2
 
 
require('fs').unlinkSync(tmp_modulePath);
 

API

In the following API, Module refers to the Module constructor, available with module.constructor or require('Module').
And module refers to a module instance, available in each module with module.

require('module-invalidate')

Enable the module-invalidate mechanism.
Any nodejs-non-internal module loaded after this call can be handled by this library.

module.invalidable

This property controls whether the module can be invalidated. By default, modules are not invalidable.

Example:

module ./myModule.js

module.invalidable = true;
module.exports = {
    foo: function() {}
}

module.invalidateByPath(path)

Invalidates the specified module by its path (same syntax and context than require()). The module should have been flagged as invalidable using module.invalidable.

Example:

require('module-invalidate');
var myModule = require('./myModule.js');
module.invalidateByPath('./myModule.js');

Module.invalidateByExports(exports)

Invalidates the module by giving its exported object. The module should have been flagged as invalidable using module.invalidable.

Example:

require('module-invalidate');
var myModule = require('./myModule.js');
module.constructor.invalidateByExports(myModule);

invalidateByExports() only invalidates one module.

module B.js

    module.invalidable = true;
    console.log('load B');
    module.exports = {
        foo: 123
    }

module A.js

    module.invalidable = true;
    console.log('load A');
    module.exports = require('./B.js');

main module index.js

    require('module-invalidate');
    var a = require('./A.js');
    console.log('invalidate');
    module.constructor.invalidateByExports(a);
    var tmp = a.foo;

output:

load A
load B
invalidate
load A

Module.invalidate()

Invalidates all nodejs-non-internal modules. Only process modules that have been flagged as invalidable using module.invalidable.

Example:

require('module-invalidate');
module.constructor.invalidate();

module.invalidate()

Invalidates the module module. The module should have been flagged as invalidable using module.invalidable.

Example:

module.invalidate();

module.unload()

Definitely unloads the module module.

module.unloadByPath(path)

Definitely unloads the module by its path (same syntax and context than require()).

Module.unloadByExports(exports)

Definitely unloads the module by giving its exported object.

module.onInvalidate(callback)

callback: function(immutable_exports)

Register a callback that will be called when the module is invalidated. The immutable_exports is a permanent reference to the current module.exports.
onInvalidate returns a function that unregisters the callback.

Gives you the opportunity to free resources created in the module.
eg. temporary files, timers, web routes, ...

The callback can return function that is called after the module is reloaded. This can help you restore your module state.

Example:

module.invalidable = true;
this.connectedUsers = [];
exports.connectUser = function(name) {
    
    this.connectedUsers.push(name);
}
 
exports.getConnectedUsers = function() {
    
    return this.connectedUsers;
}
 
module.onInvalidate(function(oldExports) {
 
    return function(newExports) {
        
        newExports.connectedUsers = oldExports.connectedUsers;
    }
});
 

How it works

1. Module.prototype.exports is overridden by a No-op forwarding ES6 Proxy that handle all accesses to module exports.
2. When a module is invalidated, it is marked as invalidated and is then reloaded on the next access (lazily).

Caveat

typeof module.exports is always 'function'

Because the library is unable to know in advance what type of value will be assigned to module.export, it choose the most generic one as ES6 Proxy target. However, (function(){}) instanceof Object === true.
As workaround, you can use instanceof against the module.exports, this will always retuns the expected result.

Example:

module ./myModule.js

module.invalidable = true;
module.exports = new Date;

main module index.js

require('module-invalidate');
var myModule = require('./myModule.js');
console.log(myModule instanceof Date); // true

Only direct variable access is handled

Example:

var foo = require('foo.js');
var bar = foo.bar;

In this case, bar will always refers to the initial foo.bar value. To avoid this, always refer bar using foo.bar.

Invalidated modules will survive with the new child-module version

In a module, module.exports will always refers to the latest version of the module.

Example:

module ./child.js

module.invalidable = true;
module.exports = {};

setInterval(function() {
    console.log(module.exports.foo);
}, 1000);

main module index.js

require('module-invalidate');

var child = require('./child.js');
child.foo = 1;
module.constructor.invalidateByExports(child);
child.foo = 2;

output

2
2
2
2
2
...

How can you help?

Give me some feedback and report bugs.

Credits

Franck Freiburger