unload-me
Self-destruct the current module from require cache
Last updated 3 years ago by bahmutov .
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unload-me

Self-destruct the current module from require cache

NPM

Build status semantic-release js-standard-style

Why

Node require function for speed only evaluates each module once and stores the result (whatever the module exports) in the module cache. Sometimes this causes problems, for example if you really need to re-evaluate the module again.

For example we might have a module that just reports if the environment variable is present

// is-foo.js
module.exports = String(process.env.FOO)

When testing this module, we might set process.env.FOO before the first test and it works

it('returns FOO', () => {
  process.env.FOO = 'test'
  const foo = require('./is-foo')
  expect(foo).to.be('test')
})

But when we write another test it suddenly fails

it('returns FOO as a string', () => {
  process.env.FOO = 42
  const foo = require('./is-foo')
  expect(foo).to.be('42')
})
// Error:
//   expect "test" to be "42"

Why is foo still the first value? Let us enable just the second test - and it passes!

it.only('returns FOO as a string', () => {
  process.env.FOO = 42
  const foo = require('./is-foo')
  expect(foo).to.be('42')
})
// passes!

This is a pesky test failure because it depends on the order of tests, something Rocha can catch, but that is the point here.

The point is that module ./is-foo is executed only once in our tests. The second time we require('./is-foo') the code inside (the single statement module.exports = String(process.env.FOO)) is NOT evaluated. Instead the cached value "test" is loaded and returned.

We can avoid caching value by switching is-foo to return a function

// is-foo
module.exports = () => String(process.env.FOO)

and every client can just execute this function.

process.env.FOO = 42
const foo = require('./is-foo')()
// foo is now '42'

But we can also easily make the module is-foo self-destruct from the require.cache to force Node module system to reload an reevaluate its code. Just add a single line to the module.

module.exports = String(process.env.FOO)
require('unload-me')

Install

Requires Node version 6 or above.

npm install --save unload-me

Use

Just call require('unload-me') at the end of the module you want to "self-destruct". It will be re-evaluated next time someone requires it.

console.log('*** WITH unload this code runs every time')
console.log('*** you call require("./with-unload")')
module.exports = 'foo'
// require 'unload-me' to remove this module
// from require.cache and force loading and
// evaluating it again
require('unload-me')

See test/demo.js for full example

Small print

Author: Gleb Bahmutov <gleb.bahmutov@gmail.com> © 2017

License: MIT - do anything with the code, but don't blame me if it does not work.

Support: if you find any problems with this module, email / tweet / open issue on Github

MIT License

Copyright (c) 2017 Gleb Bahmutov <gleb.bahmutov@gmail.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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