Custom parsers

Definitions are YAML by default. Switch the whole project to JSON, or give it a parser for any other format.

YAML#

YAML needs no configuration. Every example in these docs is YAML, and the YAML example project is a complete setup.

JSON#

Set parser to json in the configuration:

module.exports = {
  parser: 'json',
}

Every definition is then a .json file. The checkout feature from the Quick start becomes:

{
  "description": "Checkout redesign",
  "bucketBy": "userId",
  "rules": [
    {
      "key": "netherlands",
      "conditions": "netherlands",
      "percentage": 100
    },
    {
      "key": "everyone",
      "conditions": "*",
      "percentage": 25
    }
  ]
}

The JSON example project is a complete setup.

Another format#

A custom parser is an object with three properties:

Both functions are synchronous. The file path is there so a parser can say where an error is. Featurevisor checks that both exist when it loads the configuration. It writes definitions with stringify, for example during promote --apply, so a parser must write as well as read.

For TOML, smol-toml does both:

npm install --save-dev smol-toml

const toml = require('smol-toml')
module.exports = {
  parser: {
    extension: 'toml',
    parse: (content) => toml.parse(content),
    stringify: (content) => toml.stringify(content),
  },
}

The TOML example project is a complete setup.

Pick a format that can hold every value your definitions use. TOML has no null, for example. Writing a file through stringify can also change its formatting and drop comments, so check the Git diff after a command writes definitions.

Related#

• Configuration
• Projects
• Datasource, to read definitions from somewhere other than files