Mithril viewmodel

Implementation of viewmodel library for Javascript MVC framework Mithril, that is based on article on Mithril's official blog Mapping view models.

Unlike an implementation that is proposed by author of the article, this module does not store mapping from model to viewmodel in a map, but it adds "secret" unenurable read-only property to each model. Moreover it supports nested viewmodel defaults and also it does not enforce m.prop for all its fields.

Here is an example of usage:

var viewmodel = require('mithril-viewmodel.js')

// Here is defined a viewmodel with its default values.
var vm = viewmodel({
    prop1: 42,
    propObj: {  // Properties can be nested.
        prop2: 'hello',
        prop3: m.prop('')  // Function m.prop can be used.
    },
    propArr: [1, 2, 3]  // Array can be also used.
})

var model = {a: 3}

// Get a viewmodel for the model.
console.log(
    vm(model).propObj.prop2   // Prints "hello".
)

// Assign values to the viewmodel.
vm(model).propObj.prop3('initialized')
console.log(
    vm(model).propObj.prop3()  // Prints "initialized".
)

For more examples, see tests please.

Some additional notes:

• Viewmodel must be always a JS object.
• In viewmodel defaults object, all properties that are functions (means all objects obj such as typeof obj === 'function') must be instances of m.prop!
• It for example means one cannot use Date type. But one can use m.prop(new Date()). (And access is as vm(model).dateProp().)
• Hack: but you can define something like: viewmodel({key: () => keyCounter++}) to automatically assign key attributes! (And again, access them as m.prop property, e.g. vm(obj).key().)
• There is no check for circular dependencies in viewmodel defaults.
• You can define more viewmodels for one model!
• Name of a "secret" property can be configured! (Both globally as viewmodel.propName = 'pattern_%, where % is a placeholder or locally as viewmodel({}, 'secret_prop_name').)