knitr::is_word_output() to check if the current output type is word – just like knitr::is_latex_output() and knitr::is_html_output()

Question

knitr::is_latex_output() and knitr::is_html_output() allow checking if the current output type LaTex or HTML respectively.

Is there an equivalent for Word as an output format?

If not, what would be the most simple to use workaround?

---
title: "MWE for different file formats in namespace:knitr"
output:
  pdf_document: default
  html_document: default
  word_document: default
---

```{r}
if (knitr::is_html_output()) {
  cat("HTML") 
  }
if (knitr::is_latex_output()) {
  cat("LATEX") 
  }
if (knitr::is_word_output()) {
  cat("WORD")
}
## Error: 'is_word_output' is not an exported object from 'namespace:knitr'
```

Answer 1

As of knitr 1.31 (released in January 2021), you can use knitr::pandoc_to() in either of the following ways:

```{r}
if (knitr::pandoc_to("docx")) {
  cat("Word") 
}
```

```{r, include=knitr::pandoc_to("docx")}
cat("Word")
```

To conditionally output literal text content (rather than R code), it's easiest to use an asis chunk (note that we need to use the echo option instead of include):

```{asis, echo=knitr::pandoc_to("docx")}
This will only appear in Word documents.
```

```{asis, echo=knitr::pandoc_to("docx", "pdf")}
This will be appear in Word and PDF documents.
```

Historical answer

In earlier versions of knitr, you can use an internal knitr function to get the type you want:

is_word_output <- function(fmt = knitr:::pandoc_to()) {
  length(fmt) == 1 && fmt == "docx"
}