How to print htmlwidgets to HTML result inside a function?

问题

---
title: "Untitled"
output: html_document
---

```{r setup, include=FALSE}
library(DT)
xsx = function(){
  print(getOption("viewer"))
  print(datatable(data.frame(d =1)))
  1
}
xsx()
```

Inside xsx() function, DT widgets will not be rendered in HTML result. How can I get widgets print inside a function?

来源：https://stackoverflow.com/questions/35567124/how-to-print-htmlwidgets-to-html-result-inside-a-function