Rate limiting all observables by default

Question

Is there a way in knockout.js to rate limit all observables by default?

I'd like to not have to extend all my observables one by one.

Answer 1

You can create a function to use instead of ko.observable. I do this just to save typing, myself:var KOB = ko.observable;

For your case, it would be (something like):

var KOB = function (value) {
    return ko.observable(value).extend({rateLimit:500});
};

Answer 2

Monkey see, monkey do: monkey patch!

But first, let me say that AFAIK there is no way to do what you want with a Knockout feature; there is no global setting (anything like ko.globalSettings["defaultRateLimit"]) to set default rate limits for all future observables.

Nonetheless, here's a way to monkey patch Knockout in a straightforward way to do exactly as you ask. However, I'd consider this a rather late/last resort: with monkey patching you never know how it'll affect future releases of a framework. Also, this will irrevocably change ko.observable so that it does what you ask, no exceptions.

(function() {
  var originalObservableFn = ko.observable;
  ko.observable = function(x) {
    return originalObservableFn(x).extend({rateLimit: 1500});
  }
})();

var vm = {
  myValue: ko.observable("initial value")
};

ko.applyBindings(vm);

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>

Change value here: <input data-bind="textInput: myValue" autofocus /><br />
Read only version: <span data-bind="text: myValue"></span>

For a more scoped solution I'd recommend @RoyJ's solution where you create a new shorthand function to do what you want. It allows you quite a bit more control, which is great because I can't quite imagine any practical production scenario where you want all observables rateLimited, not in the least because it makes unit testing them quite a bit harder as updates become asynchronous.

A final option of course would be to fork Knockout itself, which is easy as it's source is available on GitHub.

Answer 3

You could create a function on ko.observable that would add some syntactical sugar to your code. http://knockoutjs.com/documentation/fn.html

so instead of writing ko.observable(value).extend({rateLimit: 500})

it could be possible to write ko.observable(value).limit(500)

I havent tested this yet but would be worth exploring this or possibly a custom binding data-bind="rateLimitValue: fullName"