watchModule

Usage Demo for my npm-module up2require

On a screenshot below app is started with index.js, then it calls a function every 1.5 seconds. That function is imported from a custom module which uses another function imprted from another module. Then right while the program is running I change the file open on the right ('abc' to 'abd') and save it. That submodule is immediately reimported automatically without restart and function is replaced internally with the updated version. Then I change the file in the center (11 to 12) and save it. That module is immediately reimported automatically too so the console.log(12) is called. But the function is still working as it was before.

On a next screenshot again while the app is running I change the API handler function, save the file and reload the page in browser to immediately see the changes without restarting node process.

And here is the up2require function module code itself:

const {watch} = require('fs')
const reloadingWrappers = {}

module.exports = function upgradeToUpdate(require) {
  function watchfulRequire(module, reloadUpdated) {
    if (reloadUpdated) {
      module = require.resolve(module)
      if (module in reloadingWrappers) {
        return reloadingWrappers[module]
      } else {
        watch(module, () => delete require.cache[module])

        const wrapperFn = function (...args) {
          if (new.target) return new (require(module))(...args)
          return require(module).apply(this, args)
        }

        const wrapperProxy = new Proxy(wrapperFn, {get(_, prop) {
          return require(module)[prop]
        }})
        return reloadingWrappers[module] = wrapperProxy
      }
    }
    return require(module)
  }

  require.fresh = require.cache.untilUpdate =
    module => watchfulRequire(module, true)

  Object.assign(watchfulRequire, require)

  return watchfulRequire
}