函数：
ui.Button(label, onClick, disabled, style)
A clickable button with a text label.
Arguments:
label (String, optional):
The button's label. Defaults to an empty string.
onClick (Function, optional):
A callback fired when the button is clicked. The callback is passed the button widget.
disabled (Boolean, optional):
Whether the button is disabled. Defaults to false.
style (Object, optional):
An object of allowed CSS styles with their values to be set for this widget. Defaults to an empty object.