06. Extending `{golem}`

This Vignette discusses how you can extend golem.

Project Hooks

What it is

The create_golem() function comes with a project_hook parameter, a function run just after the golem project creation. It can be used to modify the project structure automatically just after its creation.

This allows you to define custom behavior when creating golem based app, that can be used for:

Adding a different front-end template in R/app_ui.R
Changing configuration options in inst/golem-config.yml
Copying external files in inst/app/www
Removing any file from the default template
etc.

How it works

The function is called after the default project has been created, and is executed in the directory of the created package. Here is a rough step by step of what happens when a project is created with golem:

The package name is generated
The directory that will receive the package is created
Default golem template is copied and pasted
R moves to the directory of the newly created project, and runs the project_hook function
R moves back to the previous directory, and removes comments if needed
Project is open

Defining your own `project_hook`

The best way to extend golem project hook functionality is by defining this project_hook function in an external package. This will allow this function to be used inside the golem creation RStudio project creation widget:

Note that inside this widget, the function should be explicitely namespaced (pkg::fun)

The project_hook function takes three mandatory parameters, which are passed from create_golem:

path: the full path of the directory
package_name: the name of the package
... : further arguments that can be passed via create_golem

These parameters might not be used inside your own hook, but they need to be set in the hook function skeleton, for compatibility reasons.

Example

Here is an example of a function that can be used to remove the dev/ folder:

no_dev <- function(path, package_name, ...) {
  fs::dir_delete("dev")
}
create_golem("ici", project_hook = no_dev)

This one will create a CSS:

new_css <- function(path, package_name, ...) {
  css_path <- fs::path_abs("inst/app/www/custom.css")

  fs::file_create(css_path)

  write_there <- function(...) {
    write(..., file = css_path, append = TRUE)
  }

  write_there("body {")
  write_there("    background-color:red;")
  write_there("}")

  cli_cat_bullet("CSS generated")
}

create_golem("ici", project_hook = new_css)

Module templates

What it is

Module templates are a way to define your own content for creating the module script in R/. It allows to extend golem module template functionality by creating your own content inside the module file.

How it works

The function is called after the file(s) creation. Here is a step by step of what happens when the add_module function is called:

Name is created, and so is the R/ directory if needed.
The fct_ and utils_ files are created if necessary
The path to the module is generated
If the file already exists, it opens the file
If the file doesn’t exist, R creates it and the module_template function is called
File is generated, and potentially open

(Note that the module_template function is not called if the file already exists).

Defining your own `module_template`

You can then define your own function inside your golem based application, but chances are you will be defining them into your own package.

Module template functions will receive, by default, the following parameters from add_modules().

name: the name of the module
path: the path to the file in R/
export: a TRUE/FALSE set by the export param of add_module()
... further arguments

These parameters might not be used inside your own function, but they need to be set in the function skeleton, for compatibility reasons.

Example

my_tmpl <- function(name, path, export, ...) {
  # Define a template that only write the name of the
  # module in the file
  write(name, path)
}
golem::add_module(name = "custom", module_template = my_tmpl)

my_other_tmpl <- function(name, path, ...) {
  # Copy and paste a file from somewhere else
  file.copy(..., path)
}
golem::add_module(name = "custom", module_template = my_other_tmpl)

JS & CSS & SASS templates

What it is

JavaScript, CSS and Sass template allow to use your own functions to add code when creating JavaScript files, JavaScript handlers and CSS or Sass files. These templates work inside add_js_file(), add_js_handler(), add_css_file() and add_sass_file().

How it works

The function is called after the file creation. Here is a step by step of what happens when these functions are called:

Name is created
The path is generated
If the file already exists, it opens the file
If the file doesn’t exist, R creates it and the template function is called
File is generated, and potentially open

(Note that the template function is not called if the file already exists).

Defining your own `template`

You can then define your own function inside your golem based application, but chances are you will be defining them into your own package.

File template functions will receive, by default, the following parameters from the add_*() function.

path: the path to the file
... further arguments

These parameters might not be used inside your own function, but they need to be set in the function skeleton, for compatibility reasons.

Example

my_tmpl <- function(path, ...) {
  # Define a template that only write the name of the
  # module in the file
  write_there <- function(...) {
    write(..., file = path, append = TRUE)
  }

  write_there("body {")
  write_there("    background-color:red;")
  write_there("}")
}
golem::add_css_file(name = "custom", template = my_tmpl)

Turn on the maintenance mode

What it is

From time to time, you need your application to be unavailable: database update, API changes, etc. In order to keep your app running but make it unavailable, you can use a maintenance mode. When this maintenance mode is turned on, your application will be paused and a specific page will be displayed to your users.

golem comes with a default maintenance page, and you can replace it with you own page.

How to set the maintenance mode

The maintenance mode will be turned on whenever the R process detects that the GOLEM_MAINTENANCE_ACTIVE environment variable is set to TRUE.

To visualize the maintenance page locally, you can run the following:

withr::with_envvar(
  c("GOLEM_MAINTENANCE_ACTIVE" = TRUE),
  {
    golem::run_dev()
  }
)

Sys.setenv("GOLEM_MAINTENANCE_ACTIVE" = TRUE)
golem::run_dev()

If you’re deploying on Posit Connect, you can set this variable in the setup panel.

If in command line, you can also do

export GOLEM_MAINTENANCE_ACTIVE=TRUE && Rscript -e "mygolem::run_app()"

The maintenance page

golem comes with a default maintenance page, but you can override it and use your own custom page.

In order to use your own page, you need to pass either an html_document or a tagList to the with_golem_options function in run_app.R:

run_app <- function(
  onStart = NULL,
  options = list(),
  enableBookmarking = NULL,
  uiPattern = "/",
  ...
) {
  with_golem_options(
    app = shinyApp(
      ui = app_ui,
      server = app_server,
      onStart = onStart,
      options = options,
      enableBookmarking = enableBookmarking,
      uiPattern = uiPattern
    ),
    golem_opts = list(...),
    maintenance_page = tagList(
      fluidRow(
        h1("Under maintenance"),
        span("Coming soon...")
      )
    )
  )
}

or:

run_app <- function(
  onStart = NULL,
  options = list(),
  enableBookmarking = NULL,
  uiPattern = "/",
  ...
) {
  with_golem_options(
    app = shinyApp(
      ui = app_ui,
      server = app_server,
      onStart = onStart,
      options = options,
      enableBookmarking = enableBookmarking,
      uiPattern = uiPattern
    ),
    golem_opts = list(...),
    maintenance_page = shiny::htmlTemplate(
      filename = app_sys(
        "custom_maintenance_page.html"
      )
    )
  )
}

Project Hooks

What it is

How it works

Defining your own project_hook

Example

Module templates

What it is

How it works

Defining your own module_template

Example

JS & CSS & SASS templates

What it is

How it works

Defining your own template

Example

Turn on the maintenance mode

What it is

How to set the maintenance mode

The maintenance page

Defining your own `project_hook`

Defining your own `module_template`

Defining your own `template`