When comparing Knockout vs Ember, the Slant community recommends Knockout for most people. In the question“What are the best client-side JavaScript MV* frameworks?” Knockout is ranked 2nd while Ember is ranked 16th. The most important reason people chose Knockout is:
Knockout uses HTML5 data attributes to bind HTML elements to data objects in javascript. This allows more work to be done by the framework rather than requiring you to specify where data should be bound in the javascript. The data binding is very intuitive as the bindings are done within the HTML itself in the location it should be bound.
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Pros
Pro Easy data binding
Knockout uses HTML5 data attributes to bind HTML elements to data objects in javascript. This allows more work to be done by the framework rather than requiring you to specify where data should be bound in the javascript. The data binding is very intuitive as the bindings are done within the HTML itself in the location it should be bound.
Pro Easy to learn
Has a low entry barrier and an easy learning curve. It's especially easy to learn for beginners.
Pro Built in templating
Bindings in Knockout can also be used to control the generated structure of the HTML. There are bindings provided to allow for iteration and conditionals. The structure of the html reflects the structure of the data so iterative elements are bound to arrays in the data model. Having the HTML structure maintained by bindings keeps the templating simple, easy to read, and maintain.
Knockout also allows for string based templating so you can use whatever templating library you prefer.
Pro Legacy browser support
Supports a large number of browsers, including IE6.
Pro Great documentation
The excellent tutorials with built-in exercises are a great learning experience, even for people without prior MVVM and data binding experience.

Pro Lightweight and plays nicely with other libraries
Pro Dynamic models help with keeping the code simple and clean
Models in Knockout can be watched to keep the page data up to date by using observable objects. The observables notify Knockout when data is changed and automatically updates the page when this happens. By having Knockout maintain this relation, it keeps the front end code cleaner and simpler, and by enforcing a consistent pattern with observables the methodology can be more robust.
Pro Very flexible
One can do a lot of things and it keeps self references and other types of loops under control.
Pro It's only a library
Knockout does one thing, and does it well. It doesn't try to take on more than one area. It does MVVM data binding and that is it.
Pro Simple manageable modules
Using components is a great way of breaking up large modules into simpler ones.
Pro Opinionated in terms of application structure
Ember already defines the general application structure and organization for you. This was done to prevent developers from making mistakes which would needlessly over-complicate their application. While it's still possible to go out of these practices forced to developers by the Ember authors, you still have to go out of your way to force them.
Pro Ember-CLI
Ember-CLI is a very useful tool. With just a couple of commands it scaffolds the code, installs dependencies and finally compiles everything itself. It's very useful to quickstart an Ember project.
Pro Uses Handlebars
Ember's preferred templating language is Handlebars. This is mainly because Handlebars is a logic-less templating language and Ember tries to keep it's logic outside the view.
Another reason why Ember benefits from Handlebars is mostly aesthetic as Handlebar's clean syntax makes for easier to read and understand templates.
Finally, Handlebars templates are compiled instead of interpreted, which means that they are much faster to load.
Pro Convention over configuration
Ember follows the philosophy of "convention over configuration" meaning that it already has almost everything configured for you, so you just have to start coding and developing your project right away.
Pro Complete front-end stack
Ember is practically a complete full-stack front-end framework. It comes with it's own asset pipeline, router, services etc...
Pro Completely community based
Pro One of the fastest template rendering engines (new glimmer)
Pro Easy to understand documentation
The Ember Guides are well structured and very well written. The API documentation is also fantastic.
Pro Ember's Object model makes the framework extremely consistent
Most of Ember's components come from the Ember Object Model. It's the basis for views, controllers, models and even the framework itself. This means that the framework is extremely consistent since almost every component shares the same core functionalities and properties since they are all derived from the same object.
Pro Excellent routing
Route handlers for the URLs can see a wide range of possible application states, asynchronous logic in the router makes sure of Promises. And implementing makes sense.
Pro The run loop
It batches bindings and DOM updates to increase performance; if similar tasks are added to a batch, the browser would only need to process them in one single go, as compared to re-computing for each task one at a time.
Pro Excellent API
Ember's API are really easy to understand and work with. It has methods which allow you to harness complicated functionalities in an easy to understand way.
Pro New router has less boilerplate code
Ember's new router need much less boilerplate code that it previously did.
Pro Debugging tool for almost every web browser
Ember also has a debugging tool called Ember Inspector which is used for debugging the client side of your app.
Pro Works great with jQuery
You can use any of jQuery’s features.
Pro Useful bindings
EmberJS provides with an extremely handy feature of advanced bindings. With this you can not only set the path to the binding value in your app but also set in which direction you want the changes to propagate to (oneway
, single
, multiple
etc).
Pro Promises everywhere
Promises represent an eventual state in asynchronous logic. Having promises everywhere (almost) means you could write simple and modular code, using almost any API that Ember provides.
Pro Computed properties
Having custom properties in your templates is itself a huge plus but having custom computed properties is an even greater benefit, since now you can code your custom function as a property and call it from your template. Hence rendering your page exactly according to your needs.
Pro Built-in router
Ember comes with built-in routing capabilities. There's no need to install third-party plugins to be able to use routes.
Pro Auto-updating templates
If you've used handlebars (Ember.js's templating is powered by HandleBars) helper tags in your code (like {{#each}}
) you won't have to worry about updating your template each time you add/remove data from your page, Handlebars will auto update your template for you.
Cons
Con Slower than others when amount of objects grows
Knockout has a bad performance when the dealing with large amount of objects. You can see more here.
Con Can become complex once the application grows large
Knockout leaves the application structure to the developer and it can become quite complex and unmanageable in the hands of a beginner once the application grows large and complex.
Con Two way binding requires a little extra work
When allowing users to edit existing data, the two-way binding of observables means you'll need to have to save original values before they're edited, to make comparisons or revert if the user cancels the action.
Con Large library size
At 69Kb gzipped, it is one of the largest JavaScript frameworks. This means Ember might be an overkill to use on simpler projects.
Con Very opinionated
Ember (and many extensions, like Ember Data) force the implementation down specific architectural paths. These paths are what Ember believes is best practice and typically are fine, but not in all cases. This can occasionally lead to fighting with your framework which is never productive.
Con Partly unfriendly community
