Install multiple versions of a module then dynamically switch between them.

const setModuleVersion = require('dynavers')('dynavers.json')
const versions = ['1.13.1', '2.1.0-beta.24']
for(const version of versions) {
  setModuleVersion('webpack', version);
  // ...do stuff
}

As the above example hints at, this is primarily designed for testing.

npm install --save-dev dynavers

Create a JSON spec of modules to be installed, e.g. at dynavers.json:

{
  "path": "dynavers_modules",
  "versions": {
    "webpack": ["1.13.1", "2.1.0-beta.24"]
  }
}

Do not use fuzzy versions ("^0.16.0") - this will cause problems.

Next, run

./node_modules/.bin/install-module-versions dynavers.json

In this example, it will create dynavers_modules and install webpack 1.13.1 and 2.1.0-beta.24 inside the dynavers_modules directory.

To run the install automatically before your test suite (when you run npm test), add it as a "pretest" hook to your package.json:

{
  "scripts": {
    "pretest": "install-module-versions dynavers.json",
    "test": "..."
  }
}

install-module-versions will not redownload existing modules. If something went wrong, delete its directory first: rm -r dynavers_modules

The API is a single function setModuleVersion(moduleName, moduleVersion). This will ensure any subsequent require calls to that module from anywhere will use the specified version. Note this will also ensure any exports within that module will also use the specified version:

const setModuleVersion = require('dynavers')('dynavers.json')
setModuleVersion('webpack', '1.13.1')
var webpack = require('webpack')          // version 1.13.1
var Chunk = require('weback/lib/Chunk')   // will also be the 1.13.1 version

Please read the Caveats below before opting to purge the cache

You may also want to purge the Module cache so that all modules are reloaded after you have set a version. This is easily done by adding an additional boolean argument:

const setModuleVersion = require('dynavers')('dynavers.json')
const purgeCache = true
setModuleVersion('webpack', '1.13.1', purgeCache)

Alternatively you can make this the default behaviour by adding the purgeCache value in the configuration:

{
  "path": "dynavers_modules",
  "versions": {
    "webpack": ["1.13.1", "2.1.0-beta.24"]
  },
  purgeCache: true
}

In this case, you need not specify it in the setModuleVersion call.

1. This works by monkey-patching node's Module load mechanism. You may not like this.
2. The load mechanism has not been tried with all the exotic forms of package identifier that require will accept. Please let me know if any this fails.
3. Think carefully about using the purgeCache option. In most cases it is a sledgehammer to crack a nut as it forces all future require'd modules to be reloaded. Moreover, and this is important, it will not clear any in-memory modules, so you run the risk of simutaneously running multiple versions of a module. Eek!

multidep offers an alternative that specifies the version for a single require call via its multidepRequire.

This tool is based on multidep - thanks Jo Liss!
(I would have submitted a Pull Request but by the time I had changed the external API and the core mechanism, I don't think it would have been accepted).

v0.3.x

• windows support (thanks to @snadn)
• updated dependencies
• tests run node 4.x to 11.x

v0.2.x

• add purge cache options

v0.1.x

• initial release