multipart.js

(function (){

    var node = document.getElementById('myForm');

    function AppViewModel() {

        this.uiTypes = ko.observableArray([
            {"typeValue":"A", "typeLabel": "1 field type"}, 
            {"typeValue":"B", "typeLabel": "2 fields type"}
        ]);

        this.selectedType = ko.observable();
        this.showField1 = ko.observable(false);
        this.showField2 = ko.observable(false);
        this.valueField1 = ko.observable('');
        this.valueField2= ko.observable('');

    this.selectedType.subscribe(function (type) {

        if (!type){
            this.showField1(false);
            this.showField2(false);
        } else {
            this.showField1(true);
            this.showField2(type === 'B');
        }

        this.valueField1('');
        this.valueField2('');

    }, this);

    this.enableExecutionButton = ko.computed(function(){

        var a = this.showField1();
        var b = this.showField2();
        var x = this.valueField1();
        var y = this.valueField2();

        function AndAndXnor(a,b,x,y) {
          //return (a&&b && x&&y || a&&!b && x&&!y); // WORKS
          return (a&&x) && (b&&y || !b&&!y);  // WORKS
          //return (a&&x) && !(b^y); // "(b&&y || !b&&!y)" // DOES NOT WORK
        }

        return AndAndXnor(a,b,x,y);

    }, this);

    this.pseudoSubmitForm = function(formElement){
        this.selectedType('');
    }

  }

  var model = new AppViewModel();
  ko.applyBindings(model, node);
})()