HeadElement 构造函数
实现
factory HeadElement() => JS<HeadElement>(
'returns:HeadElement;creates:HeadElement;new:true',
'#.createElement(#)',
document,
"head");
factory HeadElement() => JS<HeadElement>(
'returns:HeadElement;creates:HeadElement;new:true',
'#.createElement(#)',
document,
"head");