JSFiddle - React, Tailwind, and code Playground

HTML

<a data-bind="attr: {href : '#someHash/' + getHref(10)}">Link</a>
<a href="#" data-bind="click: changeStoreHref(20)">change Link</a>

JavaScript

function viewModel()
{
    var self = this;
    self.storeHref = ko.observable('ten');
    
    self.getHref = function(id)
    {
        return ko.computed({
            read: function()
            {
                self.storeHref(id);
                return self.storeHref();
            }
        });
    };
    
    self.changeStoreHref = function(num)
    {
        self.storeHref(num);
    };
}

ko.applyBindings(new viewModel());