JSFiddle - React, Tailwind, and code Playground

HTML

<input data-bind="value: value" />
<input data-bind="value: value2"/>

<span id="isValid"></span>

JavaScript

var viewmodel = {
    value: ko.observable(0),
    value2: ko.observable(0)
};

viewmodel.isGreaterThanFive = ko.computed({
    read: function() {
        return viewmodel.value() > viewmodel.value2();
    },
    
});

viewmodel.sayHelloIfValid = function() {
    if(viewmodel.isGreaterThanFive()) {
        document.querySelector('#isValid').innerText = 'is greater than five'; 
    } else {        
        document.querySelector('#isValid').innerText = 'is less than/equal to five'; 
    }
};

viewmodel.value.subscribe(viewmodel.sayHelloIfValid.bind(viewmodel));

ko.applyBindings(viewmodel);