Big news!Introducing Socket AI - ChatGPT-Powered Threat Analysis.Learn more
Socket
Socket

once

Package Overview
Dependencies
1
Maintainers
1
Versions
7
Issues
File Explorer

Advanced tools

once

Run a function exactly one time

    1.4.0latest
    GitHub
    npm

Version published
Maintainers
1
Weekly downloads
43,656,833
increased by7.67%

Weekly downloads

Readme

Source

once

Only call a function once.

usage

var once = require('once') function load (file, cb) { cb = once(cb) loader.load('file') loader.once('load', cb) loader.once('error', cb) }

Or add to the Function.prototype in a responsible way:

// only has to be done once require('once').proto() function load (file, cb) { cb = cb.once() loader.load('file') loader.once('load', cb) loader.once('error', cb) }

Ironically, the prototype feature makes this module twice as complicated as necessary.

To check whether you function has been called, use fn.called. Once the function is called for the first time the return value of the original function is saved in fn.value and subsequent calls will continue to return this value.

var once = require('once') function load (cb) { cb = once(cb) var stream = createStream() stream.once('data', cb) stream.once('end', function () { if (!cb.called) cb(new Error('not found')) }) }

once.strict(func)

Throw an error if the function is called twice.

Some functions are expected to be called only once. Using once for them would potentially hide logical errors.

In the example below, the greet function has to call the callback only once:

function greet (name, cb) { // return is missing from the if statement // when no name is passed, the callback is called twice if (!name) cb('Hello anonymous') cb('Hello ' + name) } function log (msg) { console.log(msg) } // this will print 'Hello anonymous' but the logical error will be missed greet(null, once(msg)) // once.strict will print 'Hello anonymous' and throw an error when the callback will be called the second time greet(null, once.strict(msg))

Keywords

FAQs

Last updated on 06 Sep 2016

Did you know?

Socket installs a Github app to automatically flag issues on every pull request and report the health of your dependencies. Find out what is inside your node modules and prevent malicious activity before you update the dependencies.

Install Socket
Socket
Socket SOC 2 Logo

Product

  • Package Issues
  • Integrations
  • Docs
  • Pricing
  • FAQ
  • Roadmap

Stay in touch

Get open source security insights delivered straight into your inbox.


  • Terms
  • Privacy
  • Security

Made with ⚡️ by Socket Inc