arcgis api4.5关于创建font字体后，报错

代码贴一下。跟示例完全一致吗？
Example:
var textSymbol = {
  type: "text",  // autocasts as new TextSymbol()
  color: "white",
  haloColor: "black",
  haloSize: "1px",
  text: "You are here",
  xoffset: 3,
  yoffset: 3,
  font: {  // autocast as new Font()
    size: 12,
    family: "sans-serif",
    weight: "bolder"
  }
};