How to use the @nativescript/core/ui/button.Button function in @nativescript/core

//btn1.on("tap", () => {
    //    console.log("adding menu item");

    //    var newItem = new pageModule.MenuItem();
    //    var text =  "item " + count;
    //    newItem.text = text
    //    newItem.on("tap", () => {
    //        console.log("ITEM [" + text + "] tapped");
    //    });
    //    page.optionsMenu.addItem(newItem);
    //    count++;
    //});

    stackLayout.addChild(btn1);

    var btn2 = new buttonModule.Button();
    btn2.text = "navigate";
    btn2.on("tap", () => {
        var nextPage = "app/tests/pages/page16";
        Frame.topmost().navigate(nextPage);
    });

    stackLayout.addChild(btn2);

    page.content = stackLayout;

    return page;
}

//iconItem.icon = "~/app" + "/tests" + "/test-icon.png"; // use + to stop regex replace during build
    //iconItem.on("tap", () => {
    //    console.log("Icon item tapped");
    //});
    //page.optionsMenu.addItem(iconItem);

    //var textItem = new pageModule.MenuItem();
    //textItem.text = "SAVE";
    //textItem.on("tap", () => {
    //    console.log("Save item tapped");
    //});
    //page.optionsMenu.addItem(textItem);

    var stackLayout = new stackModule.StackLayout();
    //var count = 0;
    var btn1 = new buttonModule.Button();
    btn1.text = "add item";
    //btn1.on("tap", () => {
    //    console.log("adding menu item");

    //    var newItem = new pageModule.MenuItem();
    //    var text =  "item " + count;
    //    newItem.text = text
    //    newItem.on("tap", () => {
    //        console.log("ITEM [" + text + "] tapped");
    //    });
    //    page.optionsMenu.addItem(newItem);
    //    count++;
    //});

    stackLayout.addChild(btn1);

let expectedRemovedNodeId = 0;

    currentInspector.childNodeRemoved = (parentId, nodeId) => {
        childNodeRemovedCalled = true;
        actualRemovedNodeId = nodeId;
    };

    const stack = new StackLayout();
    stack.ensureDomNode();

    const btn1 = new Button();
    btn1.text = "button1";
    expectedRemovedNodeId = btn1._domId;
    stack.addChild(btn1);

    const btn2 = new Button();
    btn2.text = "button2";
    stack.addChild(btn2);

    stack.removeChild(btn1);
    console.log("btn2: " + btn2);

    assert(childNodeRemovedCalled, "global inspector childNodeRemoved not called.");
    assertEqual(actualRemovedNodeId, expectedRemovedNodeId);
}

export function createPage() {
    var StackLayout = new sp.StackLayout();
    var grid = new gridModule.GridLayout();
    grid.horizontalAlignment = "left";

    StackLayout.addChild(grid);

    var btn1 = new button.Button();
    btn1.text = "btn1";
    var btn2 = new button.Button();
    btn2.text = "btn2";
    var btn3 = new button.Button();
    btn3.text = "btn3";
    var btn4 = new button.Button();
    btn4.text = "btn4";

    grid.addChild(btn2);
    grid.addChild(btn3);
    grid.addChild(btn4);

    var sp1 = new sp.StackLayout();
    sp1.orientation = "horizontal";
    sp1.height = 200;

    var b1 = new button.Button();
    b1.text = "nested Btn1";
    sp1.addChild(b1);

    var b2 = new button.Button();
    b2.text = "nested Btn2";

function showReportPage(finalMessage: string) {
    const stack = new StackLayout();
    const btn = new Button();
    btn.text = "Rerun tests";
    btn.on("tap", () => runAll(testsSelector));
    stack.addChild(btn);

    const messageContainer = new TextView();
    messageContainer.editable = messageContainer.autocorrect = false;
    messageContainer.text = finalMessage;
    stack.addChild(messageContainer);

    Frame.topmost().navigate({
        create: () => {
            const page = new Page();
            page.content = stack;
            messageContainer.focus();
            page.style.fontSize = 11;
            if (platform.isAndroid) {

constructor() {
        super();

        var counter: number = 0;

        var lbl = new label.Label();
        var btn = new button.Button();
        btn.text = "Tap me!";
        btn.on(button.Button.tapEvent, (args: observable.EventData) => {
            lbl.text = "Tap " + counter++;
        });

        this.addChild(lbl);
        this.addChild(btn);

        this.className = "MyStackLayout";
    }
}

function addButton(layout: layout.StackLayout, text: "left" | "center" | "right" | "stretch") {
    var btn = new btns.Button();
    btn.text = text;
    btn.horizontalAlignment = text;
    layout.addChild(btn);
    layout.style.paddingLeft = 5;

    return btn;
}

var stackLayout = new stackModule.StackLayout();
    var btn1 = new buttonModule.Button();
    btn1.horizontalAlignment = "left";
    btn1.verticalAlignment = "top";
    btn1.marginTop = 10;
    btn1.marginRight = 0;
    btn1.marginBottom = 10;
    btn1.marginLeft = 20;
    btn1.text = "top, left";

    var btn2 = new buttonModule.Button();
    btn2.horizontalAlignment = "center";
    btn2.verticalAlignment = "middle";
    btn2.text = "center, center";

    var btn3 = new buttonModule.Button();
    btn3.horizontalAlignment = "right";
    btn3.verticalAlignment = "bottom";
    btn3.text = "bottom, right";

    var btn4 = new buttonModule.Button();
    btn4.horizontalAlignment = "stretch";
    btn4.verticalAlignment = "stretch";
    btn4.text = "stretch, stretch";

    stackLayout.addChild(btn1);
    stackLayout.addChild(btn2);
    stackLayout.addChild(btn3);
    stackLayout.addChild(btn4);

    page.content = stackLayout;

export function createPage() {
    var page = new pageModule.Page();
    var stackLayout = new stackModule.StackLayout();
    var btn1 = new buttonModule.Button();
    btn1.horizontalAlignment = "left";
    btn1.verticalAlignment = "top";
    btn1.marginTop = 10;
    btn1.marginRight = 0;
    btn1.marginBottom = 10;
    btn1.marginLeft = 20;
    btn1.text = "top, left";

    var btn2 = new buttonModule.Button();
    btn2.horizontalAlignment = "center";
    btn2.verticalAlignment = "middle";
    btn2.text = "center, center";

    var btn3 = new buttonModule.Button();
    btn3.horizontalAlignment = "right";
    btn3.verticalAlignment = "bottom";

var btn4 = new button.Button();
    btn4.text = "btn4";

    grid.addChild(btn2);
    grid.addChild(btn3);
    grid.addChild(btn4);

    var sp1 = new sp.StackLayout();
    sp1.orientation = "horizontal";
    sp1.height = 200;

    var b1 = new button.Button();
    b1.text = "nested Btn1";
    sp1.addChild(b1);

    var b2 = new button.Button();
    b2.text = "nested Btn2";
    sp1.addChild(b2);

    grid.addChild(sp1);

    gridModule.GridLayout.setColumn(btn4, 1);
    gridModule.GridLayout.setColumn(btn3, 1);
    gridModule.GridLayout.setRow(btn2, 1);
    gridModule.GridLayout.setRow(btn4, 1);

    grid.addRow(new gridModule.ItemSpec());
    grid.addRow(new gridModule.ItemSpec());
    grid.addColumn(new gridModule.ItemSpec());
    grid.addColumn(new gridModule.ItemSpec());

    var page = new Page();