cjs-loader transitively includes commonJS modules for use on the web, and is useful for developers wanting to migrate to ES6 modules who still have legacy dependencies. Go here for a demo.
We do this using just your browser, without a compile step, by implementing require()
and other methods just while loading the module code.
For users of cjs-loader, we provide load(moduleName)
that returns a Promise
of the exports.
🔥👨💻🔥 This is an interesting, successful but terrible idea and should not be used by anyone. It reqiures support for ES6 Modules 🛠️ and has only really been tested on Chrome 61+.
Usage
First, install any public modules you want to use with NPM or Yarn. Then, use the loader:
For example, to use Handlebars (as per the demo):
;
Handlebars internally fetches about ~35 modules (via require()
), which we wrap.
Implementation
- Stub out
module.exports
,require()
etc. - Load the target module as an ES6 module^1
- If a further dependency is unavailable in
require()
, throw a known exception^2 - Catch in a global handler, and load the dependency via step 2
- Retry running the target module when done
^1 more or less
^2 require()
is synchronous, so we can't block to load more code
Specific Hacks
We abuse the fact that Chrome reruns but does not need to reload script files with the same path, but a different hash. This allows for "efficient" retries. e.g.:
;;foo1 !== foo2 // not the same, but only caused one network request
TODO: document more hacks
Notes
Things that we can't fix:
-
Don't use this in production. It's horrible.
-
Modules can't really determine their path, so if one of your dependenies is from a 302 etc, all bets are off
-
Runtime
require()
(i.e., not run on initial import) calls will fail if the code isn't available
TODOs
Things that we can fix:
-
Built-in Node packages don't work (
fs
,path
etc) -
We should coalesce multiple failures to
require()
(just returnnull
until an actual error occurs) and request further code in parallel -
This code is forked from cjs-faker, and still supports AMD, but calling an unplanned
require()
from withindefine()
doesn't work yet