Plugin development #

Note: plugin APIs is experimental and we welcome any feedback.

Earl Plugins can:

• Attach new matchers to expect
• Attach new validators to Exception class
• Add new smartEq validation rules that are used internally to compare values

A plugin is an object conforming to the PluginConfig interface:

export interface PluginConfig {
  matchers?: Record<string, DynamicMatcher>
  validators?: Record<string, DynamicValidator<any>>
  smartEqRules?: ReadonlyArray<SmartEqRule>
}

export type DynamicValidator<T> = (
  this: Expectation<T>,
  ...args: any[]
) => void | Promise<void>
export type DynamicMatcher = (...args: any[]) => any // real type should be Matcher but can be cast to anything for improved DX
export type SmartEqRule = (
  actual: any,
  expected: any,
  strict: boolean,
) => SmartEqResult | undefined

This type and other necessities for plugin development are exposed in earljs/internal module.

Typings #

Plugins should provide type information by tweaking earl's public interfaces but if you use TypeScript to develop your plugin it can be done automatically.

Examples #

• Plugin example
• Example of using plugin