JSFiddle - React, Tailwind, and code Playground

JavaScript

var VM = function() {
        this.isValid1 = ko.observable(false);
        this.isValid2 = ko.observable(false);
        this.isValid3 = ko.observable(false);
        this.isValid4 = ko.observable(false);

        this.isAllValid = ko.computed(function() {
            return this.isValid1() && this.isValid2() && this.isValid3() && this.isValid4();
        }, this);
};

var vm = new VM();

vm.isValid1(true);
vm.isValid2(true);
vm.isValid3(true);
vm.isValid4(true);

alert(vm.isAllValid());