# Continuously preview the HTML output of a book using the servr package

When any files are modified or added to the book directory, the book
will be automatically recompiled, and the current HTML page in the
browser will be refreshed. This function is based on
`servr::`[`httw()`](https://rdrr.io/pkg/servr/man/httd.html) to
continuously watch a directory.

## Usage

``` r
serve_book(
  dir = ".",
  output_dir = "_book",
  preview = TRUE,
  in_session = TRUE,
  quiet = FALSE,
  ...
)
```

## Arguments

- dir:

  The root directory of the book (containing the Rmd source files).

- output_dir:

  The directory for output files; see
  [`render_book()`](https://pkgs.rstudio.com/bookdown/reference/render_book.md).

- preview:

  Whether to render the modified/added chapters only, or the whole book;
  see
  [`render_book()`](https://pkgs.rstudio.com/bookdown/reference/render_book.md).

- in_session:

  Whether to compile the book using the current R session, or always
  open a new R session to compile the book whenever changes occur in the
  book directory.

- quiet:

  Whether to suppress output (e.g., the knitting progress) in the
  console.

- ...:

  Other arguments passed to
  `servr::`[`httw()`](https://rdrr.io/pkg/servr/man/httd.html) (not
  including the `handler` argument, which has been set internally).

## Details

For `in_session = TRUE`, you will have access to all objects created in
the book in the current R session: if you use a daemonized server (via
the argument `daemon = TRUE`), you can check the objects at any time
when the current R session is not busy; otherwise you will have to stop
the server before you can check the objects. This can be useful when you
need to interactively explore the R objects in the book. The downside of
`in_session = TRUE` is that the output may be different with the book
compiled from a fresh R session, because the state of the current R
session may not be clean.

For `in_session = FALSE`, you do not have access to objects in the book
from the current R session, but the output is more likely to be
reproducible since everything is created from new R sessions. Since this
function is only for previewing purposes, the cleanness of the R session
may not be a big concern. You may choose `in_session = TRUE` or `FALSE`
depending on your specific applications. Eventually, you should run
[`render_book()`](https://pkgs.rstudio.com/bookdown/reference/render_book.md)
from a fresh R session to generate a reliable copy of the book output.