Apps configuration

StaticDeploy allows static applications to be configured at runtime, i.e. when StaticDeploy serves them. Its strategy for doing so is very simple, and consists in injecting into html pages a javascript snippet defining a configuration object as a global variable (window.APP_CONFIG) that the application code can then read.

A configuration object is a json (string, string) dictionary. Each entrypoint has a configuration object associated with it, which will be injected into the html pages of the entrypoint's bundle. The configuration object can either be specific to the entrypoint, or be the default configuration object of the entrypoint's app (both are defined by you, the StaticDeploy admin).

The configuration snippet is injected into an html page as content of a <script> element with id app-config found in the page. If the page doesn't contain any such element, nothing is injected.

StaticDeploy adds the following variables to the injected configuration object:

  • BASE_PATH: the base path of the entrypoint at which the html page is being served

Example

Suppose you have a bundle example-app:master containing the following /index.html file: 

<head>
  <title>Example app</title>
  <script id="app-config"></script>
  <script>
    // App code which accesses the configuration object
    console.log(window.APP_CONFIG);
  </script>
</head>

You deploy the bundle to entrypoint example-app.com/base-path/, for which you have defined the following configuration object: 

{
  "EXAMPLE_CONFIG_KEY": "EXAMPLE_CONFIG_VALUE"
}

When you request http://example-app.com/base-path/index.html you get the following html as response: 

<head>
  <title>Example app</title>
  <script id="app-config">
    window.APP_CONFIG = {
      // Configuration variables defined on the entrypoint
      EXAMPLE_CONFIG_KEY: "EXAMPLE_CONFIG_VALUE",
      // Configuration variables added by StaticDeploy
      BASE_PATH: "/base-path/",
    };
  </script>
  <script>
    // App code which accesses the configuration object
    console.log(window.APP_CONFIG);
  </script>
</head>

Configuring the app during development

You have a few different possibilities to inject configuration into your apps during development.

Basic approach

A very quick and simple approach is to define a default window.APP_CONFIG for development directly inside the script: 

<script id="app-config">
  /* Development values */
  window.APP_CONFIG = { ... };
</script>

StaticDeploy will replace it on serve with the correct configuration of the served entrypoint.

Flexible approach

Another more complex but more flexible approach is to use the src attribute of the app-config script, pointing it to something that returns a configuration snippet. One such thing is the dev-config-server provided by @staticdeploy/app-config, which generates the configuration snippet from variables defined in a .env file and serves it at //localhost:3456/app-config.js. 

<script id="app-config" src="//localhost:3456/app-config.js"></script>

The src approach is supported by StaticDeploy which strips the attribute from the <script> element when serving it.

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