Esm: Unable to mock dynamic import

[deepsweet]

Hi.

After I failed with proxyquire and mock-require I tried to narrow down the issue:

import Module from 'module'

const originalLoad = Module._load

Module._load = (request, ...rest) => {
  if (request === 'target') {
    console.log('!!!')

    return {}
  }

  return originalLoad(request, ...rest)
}

import('target').catch(console.error)

{ Error: Cannot find module 'target'
    at module.exports.t.a (node_modules/esm/esm.js:1:160550)
    at node_modules/esm/esm.js:1:113726
    at module.exports.t.a (node_modules/esm/esm.js:1:113805)
    at module.exports.t.a (node_modules/esm/esm.js:1:134550)
    at I (node_modules/esm/esm.js:1:179469)
    at Immediate._onImmediate (node_modules/esm/esm.js:1:178466)
    at runCallback (timers.js:794:20)
    at tryOnImmediate (timers.js:752:5)
    at processImmediate [as _immediateCallback] (timers.js:729:5) code: 'MODULE_NOT_FOUND' }

It feels like esm is somehow checking for module existence by itself before it goes to Module._load or something. Totally not sure about the internal mechanics, but it works fine if I use plain CJS require instead of dynamic import.

[jdalton]

Hi @deepsweet!

I can totally support this.

[deepsweet]

Oh. Please do, if it's really doable :) Going to face a lot of dynamic imports mocking in tests since I loved esm loader.

[jdalton]

I've just added a scenario test to ensure mock-require and require-inject work with esm.
_(at the same time even)_ 😲😎

Update:

v3.0.29 is released 🎉

[cabbiepete]

FWIW For anyone else that finds this when looking for a mocking solution I found the package mocku https://www.npmjs.com/package/mocku very simple to setup and use.

It works a lot like the requireInject example above but I got it working first time vs struggling with the documentation of require-inject.

I like that esm is first class for mocku, although mocku is a very new library at this stage.

[deepsweet]

It's written by me in the wake of all the mocking related issues I've reported and jdalton has fixed 😁 Glad you found it useful.