once 1.4.0

"once" is a JavaScript utility available via npm, designed to ensure a function is only executed a single time. This helps to prevent duplication of function calls, which can be particularly useful in scenarios where you need to ensure a process such as event handling, data loading, or an API call is only actioned a single time.

To use "once", first you need to install it via npm using npm install once. You can then require('once') in your JavaScript file and use it to wrap the function you want to be executed only once.

Here's an example of using "once":

var once = require('once')

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

"once" can also add to the Function.prototype, ensuring the function is called only once. This feature can be enabled by calling require('once').proto().

// this only needs 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)
}

The utility also provides a 'once.strict' function to enforce that a function can only be called once. This is particularly useful for debugging, as it will throw an error if a function is attempted to be called more than once. This can help identify logical errors in your code.

// once.strict will print 'Hello anonymous' 
// and throw an error when the callback will be called the second time
greet(null, once.strict(msg))

The documentation for "once" can be found in the readme of their GitHub repository. It provides a comprehensive guide on how to use the utility, the functions it offers and the relevant syntax to ensure correct usage.