jsclass

Comparable

Comparable is a module that helps you manipulate objects that can be ordered relative to each other. It is designed to work exactly like Comparable in Ruby, only without the nice method names like "<=" that Ruby allows.

// In the browser
JS.require('JS.Comparable', function(Comparable) { ... });

// In CommonJS
var Comparable = require('jsclass/src/comparable').Comparable;

To use it, your class must define an instance method called compareTo, that tells it how to compare itself to other objects. As an example, let’s create a class to represent to-do list items. These can be ordered according to their priority.

var TodoItem = new Class({
    include: Comparable,

    initialize: function(task, priority) {
        this.task = task;
        this.priority = priority;
    },

    // Must return -1 if this object is 'less than' other, +1 if it is
    // 'greater than' other, or 0 if they are equal
    compareTo: function(other) {
        if (this.priority < other.priority) return -1;
        if (this.priority > other.priority) return 1;
        return 0;
    }
});

TodoItem now has the following instance methods:

• lt(other) – returns true iff the receiver is less than other
• lte(other) – returns true iff the receiver is less than or equal to other
• gt(other) – returns true iff the receiver is greater than other
• gte(other) – returns true iff the receiver is greater than or equal to other
• eq(other) – returns true iff the receiver is equal to other
• between(a,b) – returns true iff the receiver is between a and b inclusive
• compareTo(other) – returns -1/0/1 to indicate result of comparison

TodoItem also has a class method called compare that you should use for sorting.

Let’s create some items and see how they behave:

var items = [
    new TodoItem('Go to work', 5),
    new TodoItem('Buy milk', 3),
    new TodoItem('Pay the rent', 2),
    new TodoItem('Write code', 1),
    new TodoItem('Head down the pub', 4)
];

items[2].lt(items[1])   // -> true
items[0].gte(items[3])  // -> true
items[4].eq(items[4])   // -> true
items[1].between(items[3], items[4])  // -> true

items.sort(TodoItem.compare)
// -> [
//        {task: 'Write code', ...},
//        {task: 'Pay the rent', ...},
//        {task: 'Buy milk', ...},
//        {task: 'Head down the pub', ...},
//        {task: 'Go to work', ...}
//    ]