How do you increment a knockout.js observable?

Question

I'm finding this a strange place to be at a bit of a loss, but if I cant' do this:

koObserv(koObserv() + 1);

and a method is not provided, am I forced to do:

koObserv = ko.observable(koObserv() + 1)

This seems really clumsy.. is there another way that I'm missing?

Answer 1

Here is a fiddle that demonstrates incrementing:

http://jsfiddle.net/jearles/LbPDK/

As you can see self.num(self.num() + 1); does work.

Answer 2

you could abstract these logic into an extend observable

ko.observable.fn.increment = function (value) {
    this(this() + (value || 1));
};

var counter = ko.observable(0);
console.log(counter()); // 0

counter.increment();
console.log(counter()); // 1

counter.increment();
console.log(counter()); // 2

counter.increment(5);
console.log(counter()); // 7

Answer 3

I would suggest you to, if you use a lot of increment, create some helper function to do the increment and pass it the reference of your observable. You end up with more readable code.

JS:

var increment = function (observable) {
    observable(observable() + 1);
};

var MyViewModel = function () {
    this.num1 = ko.observable(0);

    this.incrementNum = function (observable) {
        // passing the observable by reference to the helper function
        increment(observable);
    }
}

HTML:

<button data-bind="click: incrementNum.bind($root, num1)">

JSFiddle example