Notoriously Pedantic Magistrate

    thunky
    DefinitelyTyped icon, indicating that this package has TypeScript declarations provided by the separate @types/thunky package

    1.1.0 • Public • Published

    thunky

    Delay the evaluation of a paramless async function and cache the result (see thunk).

    npm install thunky
    

    build status

    Example

    Let's make a simple function that returns a random number 1 second after it is called for the first time

    var thunky = require('thunky')
     
    var test = thunky(function (callback) { // the inner function should only accept a callback
      console.log('waiting 1s and returning random number')
      setTimeout(function () {
        callback(Math.random())
      }, 1000)
    })
     
    test(function (num) {  // inner function is called the first time we call test
      console.log(num) // prints random number
    })
     
    test(function (num) {  // subsequent calls waits for the first call to finish and return the same value
      console.log(num) // prints the same random number as above
    })

    Lazy evaluation

    Thunky makes it easy to implement a lazy evaluation pattern.

    var getDb = thunky(function (callback) {
      db.open(myConnectionString, callback)
    })
     
    var queryDb = function (query, callback) {
      getDb(function (err, db) {
        if (err) return callback(err)
        db.query(query, callback)
      })
    }
     
    queryDb('some query', function (err, result) { ... } )
     
    queryDb('some other query', function (err, result) { ... } )

    The first time getDb is called it will try do open a connection to the database. Any subsequent calls will just wait for the first call to complete and then call your callback.

    A nice property of this pattern is that it easily allows us to pass any error caused by getDb to the queryDb callback.

    Error → No caching

    If the thunk callback is called with an Error object as the first argument it will not cache the result

    var fails = thunky(function (callback) {
      console.log('returning an error')
      callback(new Error('bad stuff'))
    })
     
    fails(function (err) { // inner function is called
      console.log(err)
    });
     
    fails(function (err) { // inner function is called again as it returned an error before
      console.log(err)
    })

    Promise version

    A promise version is available as well

    var thunkyp = require('thunky/promise')
     
    var ready = thunkyp(async function () {
      // ... do async stuff
      return 42
    })
     
    // same semantics as the callback version
    await ready()

    License

    MIT

    Install

    npm i thunky

    DownloadsWeekly Downloads

    10,377,750

    Version

    1.1.0

    License

    MIT

    Unpacked Size

    7.76 kB

    Total Files

    7

    Last publish

    Collaborators

    • feross
    • mafintosh