ForrestJS API » The App Config

ForrestJS API » The App Config

The App Config

A ForrestJS App shares a piece of memory where to collect any boot-time configuration and the API to access and manipulate it.

Provide the App's Configuration

You can use the declarative style where the settings are provided as a simple JavaScript object:

forrestjs.run({
  settings: {
    key: 'value',
  },
});

💻 Live on CodeSandbox:
https://codesandbox.io/s/app-config-declarative-dcqg5?file=/src/index.js:1101-1162

Or run a more rich settings composition, using an asynchronous function that can perform calculations, or maybe fetch some secrects from a vault:

forrestjs.run({
  settings: async () => {
    return {
      key: 'value',
    };
  },
});

💻 Live on CodeSandbox:
https://codesandbox.io/s/app-config-programmatic-bbhg7?file=/src/index.js:53-484

Reading From The Configuration

Use getConfig(key [, defaultValue]) to read from the App's configuration:

const planet = getConfig('user.address.planet');

💻 Live on CodeSandbox:
https://codesandbox.io/s/app-config-declarative-dcqg5?file=/src/index.js:310-386

You can be very specific about the info you ask as the path is formally checked and the getConfig() will throw an error in case the required path does not exists. This behavior helps you to avoid typos in the data-paths you plan to access.

try {
  getConfig('foo.bar.does.not.exists');
} catch (err) {
  console.log(err.message);
}

💻 Live on CodeSandbox:
https://codesandbox.io/s/app-config-declarative-dcqg5?file=/src/index.js:632-807

Default Values

It may happen that you want to apply a default value to a non existing config key.

This could be useful in case you want to set a loose dependency on an optional Service or Feature that may or may not provide some information:

const optData = getConfig('opt.data', 'foobar');

When using the default value you (obviously) loose the strict check on the path's correctness. Be careful with that!

💻 Live on CodeSandbox:
https://codesandbox.io/s/app-config-declarative-dcqg5?file=/src/index.js:813-1037

Array Support

The set/get config is based on a small utility called dotted. There is a primitive support for accessing data in array format. Please refer to the documentation in the NPM page.