Nightingale Posing Mischievously


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    Extend objects using the mixin pattern with methods that are chosen when called (using a condition defined with each mixin). This is useful for loose-schema models that might have different validation rules or other functionality that depends on its state (like a type id).

    $ npm install conditional-mixin --save


    var mixin = require('conditional-mixin');
    var Animal = function(type) { this.type = type; };
    Animal.prototype.hello = function() { console.log('I am an animal.') };
    mixin.apply(Animal, require('./cat.js'));
    mixin.apply(Animal, require('./dog.js'));
    // cat.js
    module.exports = mixin.define({type: 1}, {
        hello: function() {
            console.log('I am a cat.');
    // dog.js
    module.exports = mixin.define({type: 2}, {
        hello: function() {
            console.log('I am a dog.');
    console.log((new Animal(0)).hello()); // "I am an animal."
    console.log((new Animal(1)).hello()); // "I am a cat."
    console.log((new Animal(2)).hello()); // "I am a dog."

    Test Types

    When defining a mixin the first argument repesents the condition that should be met in order to use the mixin methods. It can be any of these styles:

    • Callback (function) – Return true or false from a function to indiciate if the mixin is to be applied. The this context will be the same as the candidate method.
    • Property List (object) – Each property will be checked against the instance for strict equality. Nested properties can be tested using keys like: "a.b.c".
    • Omitted – Operates like a regular mixin. All properties / functions are applied.

    Additional Notes

    Accessing Original Methods / Properties

    From any of the mixin methods, there is a special _mixinParent() function that returns all properties before any mixins were applied. Any functions will be bound to the current instance to prevent the need for manual binding.

    module.exports = mixin.define({type: 2}, {
        hello: function() {
            console.log('I am a dog.');
            console.log('More generically, I am a:');


    $ npm test


    Copyright © 2014 Brian Reavis & Contributors

    Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at:

    Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


    npm i conditional-mixin

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    Apache License v2.0

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