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thunky

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thunky

delay the evaluation of a paramless async function and cache the result

    1.1.0latest

Version published
Maintainers
2
Weekly downloads
10,298,060
decreased by-14.62%

Weekly downloads

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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

Keywords

FAQs

What is thunky?

delay the evaluation of a paramless async function and cache the result

Is thunky popular?

The npm package thunky receives a total of 8,276,979 weekly downloads. As such, thunky popularity was classified as popular.

Is thunky well maintained?

We found that thunky demonstrated a not healthy version release cadence and project activity because the last version was released a year ago.It has 2 open source maintainers collaborating on the project.

Last updated on 14 Oct 2019

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