防止在特定情况下设置可观察量

Question

Is it possible to overload the setter on observable to prevent setting its value in some cases? Say with a function which will trigger before setting observable, like this:

function(value) {
    if (value === 'ok') {
        proceed; //set value of observable
    } else {
        break; //do not set observable
    }
}

I guess that it can be achieved by using subscriptions, but I am not fully aware how.

Not that I'm using knockout 3.0.

Answer 1

You can use writable computed observable with read and write functions:

var _prop = ko.observable();

var prop = ko.computed({
    read: function() {
        return _prop();
    },
    write: function(value ) {
        if (value === 'ok') {
            _prop(value); //set value of observable
        }
        // else do not set observable
    }
});