Package Exports

before-after-hook

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Readme

before-after-hook

asynchronous hooks for internal functionality

Usage

// instantiate hook API
const hook = new Hook()

// Create a hook
function getData (options) {
  return hook('get', options, fetchFromDatabase)
    .then(handleData)
    .catch(handleGetError)
}

// register before/error/after hooks.
// The methods can be async or return a promise
hook.before('get', beforeHook)
hook.error('get', errorHook)
hook.after('get', afterHook)

getData({id: 123})

The methods are executed in the following order

beforeHook
fetchFromDatabase
afterHook
getData

beforeHook can mutate options before it’s passed to fetchFromDatabase.

If an error is thrown in beforeHook or fetchFromDatabase then errorHook is called next.

If afterHook throws an error then handleGetError is called instead of getData.

If errorHook throws an error then handleGetError is called next, otherwise afterHook and getData.

You can also use hook.wrap to achieve the same thing as shown above:

hook.wrap('get', async (getData, options) => {
  await beforeHook(options)

  try {
    const result = getData(options)
  } catch (error) {
    await errorHook(error, options)
  }

  await afterHook(result, options)
})

Install

npm install before-after-hook

Or download the latest before-after-hook.min.js.

Constructor

The Hook constructor has no options and returns a hook instance with the methods below

const hook = new Hook()

hook.api

Use the api property to return the public API:

hook.before()
hook.after()
hook.error()
hook.wrap()
hook.remove()

That way you don’t need to expose the hook() method to consumers of your library

hook()

Invoke before and after hooks. Returns a promise.

hook(nameOrNames, [options,] method)

Argument	Type	Description	Required
`name`	String or Array of Strings	Hook name, for example `'save'`. Or an array of names, see example below.	Yes
`options`	Object	Will be passed to all before hooks as reference, so they can mutate it	No, defaults to empty object (`{}`)
`method`	Function	Callback to be executed after all before hooks finished execution successfully. `options` is passed as first argument	Yes

Resolves with whatever method returns or resolves with. Rejects with error that is thrown or rejected with by

Any of the before hooks, whichever rejects / throws first
method
Any of the after hooks, whichever rejects / throws first

Simple Example

hook('save', record, function (record) {
  return store.save(record)
})
// shorter:  hook('save', record, store.save)

hook.before('save', function addTimestamps (record) {
  const now = new Date().toISOString()
  if (record.createdAt) {
    record.updatedAt = now
  } else {
    record.createdAt = now
  }
})

Example defining multiple hooks at once.

hook(['add', 'save'], record, function (record) {
  return store.save(record)
})

hook.before('add', function addTimestamps (record) {
  if (!record.type) {
    throw new Error('type property is required')
  }
})

hook.before('save', function addTimestamps (record) {
  if (!record.type) {
    throw new Error('type property is required')
  }
})

Defining multiple hooks is helpful if you have similar methods for which you want to define separate hooks, but also an additional hook that gets called for all at once. The example above is equal to this:

hook('add', record, function (record) {
  return hook('save', record, function (record) {
    return store.save(record)
  })
})

hook.before()

Add before hook for given name. Returns hook instance for chaining.

hook.before(name, method)

Argument	Type	Description	Required
`name`	String	Hook name, for example `'save'`	Yes
`method`	Function	Executed before the wrapped method. Called with the hook’s `options` argument. Before hooks can mutate the passed options before they are passed to the wrapped method.	Yes

Example

hook.before('save', function validate (record) {
  if (!record.name) {
    throw new Error('name property is required')
  }
})

hook.error()

Add error hook for given name. Returns hook instance for chaining.

hook.error(name, method)

Argument	Type	Description	Required
`name`	String	Hook name, for example `'save'`	Yes
`method`	Function	Executed when an error occurred in either the wrapped method or a `before` hook. Called with the thrown `error` and the hook’s `options` argument. The first `method` which does not throw an error will set the result that the after hook methods will receive.	Yes

Example

hook.error('save', function (error, options) {
  if (error.ignore) return
  throw error
})

hook.after()

Add after hook for given name. Returns hook instance for chaining.

hook.after(name, method)

Argument	Type	Description	Required
`name`	String	Hook name, for example `'save'`	Yes
`method`	Function	Executed after wrapped method. Called with what the wrapped method resolves with the hook’s `options` argument.	Yes

Example

hook.after('save', function (result, options) {
  if (result.updatedAt) {
    app.emit('update', result)
  } else {
    app.emit('create', result)
  }
})

hook.wrap()

Add wrap hook for given name. Returns hook instance for chaining.

hook.wrap(name, method)

Argument	Type	Description	Required
`name`	String	Hook name, for example `'save'`	Yes
`method`	Function	Receives both the wrapped method and the passed options as arguments so it can add logic before and after the wrapped method, it can handle errors and even replace the wrapped method altogether	Yes

Example

hook.wrap('save', async function (saveInDatabase, options) {
  if (!record.name) {
    throw new Error('name property is required')
  }

  try {
    const result = await saveInDatabase(options)

    if (result.updatedAt) {
      app.emit('update', result)
    } else {
      app.emit('create', result)
    }

    return result
  } catch (error) {
    if (error.ignore) return
    throw error
  }
})

hook.remove()

Removes hook for given name. Returns hook instance for chaining.

hook.remove(name, hookMethod)

Argument	Type	Description	Required
`name`	String	Hook name, for example `'save'`	Yes
`beforeHookMethod`	Function	Same function that was previously passed to `hook.before()`, `hook.error()`, `hook.after()` or `hook.wrap()`	Yes

Example

hook.remove('save', validateRecord)

License

Apache 2.0