Knockout绑定问题，只能使用匿名函数获取值

function MyViewModel() {
    this.myData = ko.observable('Hello, Knockout!');
}

var viewModel = new MyViewModel();
ko.applyBindings(viewModel);

<div data-bind="text: function() { return myData().toUpperCase(); }"></div>

function MyViewModel() {
    this.myData = ko.observable('Hello, Knockout!');
    this.formattedData = ko.computed(function() {
        return this.myData().toUpperCase();
    }, this);
}

var viewModel = new MyViewModel();
ko.applyBindings(viewModel);

<div data-bind="text: formattedData"></div>

ko.bindingHandlers.uppercase = {
    update: function(element, valueAccessor) {
        var value = ko.unwrap(valueAccessor());
        element.textContent = value.toUpperCase();
    }
};

function MyViewModel() {
    this.myData = ko.observable('Hello, Knockout!');
}

var viewModel = new MyViewModel();
ko.applybindings(viewModel);

<div data-bind="uppercase: myData"></div>