Exploring the View-Model declaration in Knockout.js: Unveiling two distinct approaches

For my latest project, I am utilizing Knockout.js to create a dynamic client application with numerous knockout.js ViewModels. During development, I came across two distinct methods of creating these ViewModels. First method:

function AppViewModel() {
this.firstName = ko.observable("Bert");
this.lastName = ko.observable("Bertington");}

Second method:

var appViewModel = {
this.firstName = ko.observable("Bert"),
this.lastName = ko.observable("Bertington")};

I'm curious if there are any significant differences between these two approaches for declaring ViewModels. The examples on the official Knockout.js page utilize the first method, while third party frameworks such as Knockout-validations.js use the second method. Which one should I go with? Are there specific advantages to using one over the other?

After some testing, I discovered that opting for the first method prevents me from efficiently implementing the Knockout-validations.js framework. This has left me feeling quite perplexed. Any insights or suggestions would be greatly appreciated.

Thank you.

Answer №1

One way to define an object constructor is by creating the structure but not actually instantiating a new object, allowing you to pass in arguments. This method is preferable when creating multiple objects/models as it results in less cumbersome code compared to the alternative.

The second approach involves using object initializer syntax to directly instantiate a new object with specified fields. While this may lead to smaller code size, it is more suitable for situations where two objects share similar structures. In such cases, opting for the first method would be more efficient.

There is no strict rule preventing the use of one over the other. Simply create a new object and integrate it wherever needed.

For example:

function AppViewModel(fName, lName) {
    var self = this;
    self.firstName = ko.observable(fName);
    self.lastName = ko.observable(lName);
}
...
var appViewModel = new AppViewModel("Bert", "Bertington");

results in the same object as:

var appViewModel = {
    this.firstName = ko.observable("Bert"),
    this.lastName = ko.observable("Bertington")
};

The first method allows for the creation of multiple instances of AppViewModel, like new AppViewModel("Joe", "Shmoe").

Answer №2

The distinction mentioned is not exclusive to knockout or its libraries, but rather a subject of ongoing discussion within the JavaScript community at large. Renowned JavaScript expert Douglas Crockford has written two articles presenting contrasting views on this issue:

  • Classical Style
  • Prototypal Style

After reviewing various online discussions, blog posts, and interactions with fellow JavaScript developers, it seems that the preference is leaning towards adopting the prototypal style. Ultimately, the choice between the two styles comes down to personal preference. However, it is worth noting that the Knockout-Validation library was likely designed with the classical style in mind, making it easier to integrate with said library. On the other hand, using the prototypal approach may present challenges when working with this specific library.

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