multiple modules with the same name

James Burke jrburke at
Mon Jan 27 17:13:04 PST 2014

On Mon, Jan 27, 2014 at 3:14 PM, John Barton <johnjbarton at> wrote:
> On Mon, Jan 27, 2014 at 2:50 PM, Sam Tobin-Hochstadt <samth at>
> wrote:
>> Imagine that some browser has an ok-but-not-complete implementation of
>> the X library, but you want to use jQuery 17, which requires a better
>> version.  You need to be able to replace X with a polyfilled update to
>> X, and then load jQuery on top of that.
>> Note that this involves indirect access in the same library (jQuery)
>> to two versions of X (the polyfill and the browser version), which is
>> why I don't think Marius's worry is fixable without throwing out the
>> baby with the bathwater.
> Guy Bedford, based on experiences within the requirejs and commonjs worlds,
> has a much better solution for these scenarios. (It's also similar to how
> npm works).
> Your jQuery should depend upon the name X, but you Loader should map the
> name X when loaded by jQuery to the new version in Loader.normalize(). The
> table of name mappings can be configured at run time.
> For example, if some other code depends on X at 1.6 and jQuery needs X at 1.7,
> they each load exactly the version they need because the normalized module
> names embed the version number.

In the AMD world, map config has been sufficient for these needs[1].

As a point of reference, requirejs only lets the first module
registration win, any subsequent registrations for the same module ID
are ignored. “ignore" was chosen over “error" because with multiple
module bundles, the same module ID/definition could show up in two
different bundles (think multi-page apps that have a “common” and
page-specific bundles).

I do not believe that case should trigger an error. It is just
inefficient, and tooling for bundles could offer to enforce finding
these inefficiencies vs the browser stopping the app from working by
throwing an error.

It is true that the errors introduced by “ignore” could be harder to
detect given that things may mostly work. The general guide in this
case for requirejs was to be flexible in the same spirit of HTML

Redefinition seems to allow breaking the expectation that the module
value for a given normalized ID is always the same.

When the developer wants to explicitly orchestrate different module
values for specific module ID sets, something like AMD’s map config is
a good solution as it is a more declarative statement of intent vs
code in a module body deciding to redefine.

Also, code in module bodies do not have enough information to properly
redefine for a set of module IDs like map config can. Map config has
been really useful for supporting two different versions of a module
in an app, and for providing mocks to certain modules for unit

Given what has been said so far for use cases, I would prefer either
“ignore” or “error” over redefinition, with a preference of “ignore”
over “error" based on the above.



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