JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <p>
    <!-- ko foreach: fields -->
    <input data-bind="value: $data.value" />
    <!-- /ko -->
    <span data-bind="text: sum"></span>
    </p>
</div>

JavaScript

function vm(){
    var self = this;
    
    var ObsNumber = function(i) {
        this.value = ko.observable(i);
    }
    
    self.fields = ko.observableArray([new ObsNumber(1) ,
                                      new ObsNumber(2)]);
    
    self.sum = ko.computed(function(){
        var total = 0;
        ko.utils.arrayForEach(self.fields(), function(item) {
            //debugger;
            total += parseFloat(item.value());
        });
        return total;
    });
};

ko.applyBindings(new vm());