Added UMD

[redexp]

No braking changes, but now this file can be treat as module for commonjs or require.js or have regular global Janus var

I used this UMD template https://github.com/umdjs/umd/blob/master/templates/returnExports.js

[januscla]

Thanks for your contribution, @redexp! Please make sure you sign our CLA, as it's a required step before we can merge this.

[redexp]

Another pros - you can define as many private var as you need. Like that var defaultExtension that I assumed should be private, but right now it's in global scope and could be overwritten in some other file.

[lminiero]

I'm not knowledgeable about JavaScript enough to have an opinion: I only care that this doesn't break existing demos. I'll leave @atoppi to evaluate if this could cause us problems. I do notice that this apparently didn't pass our linter check on Github Actions, though.

[redexp]

linter errors on typeof define I think if I change it to typeof root.define then it should pass linter

[atoppi]

Please address the linting issues.

I see nothing wrong about the PR.
If @lminiero is fine with moving the Janus definition from the top level to an immediately invoked function then we're good to go.

[redexp]

@atoppi

    28:38  error    'define' is not defined                       no-undef
    29:3   error    'define' is not defined                       no-undef
    30:43  error    'module' is not defined                       no-undef
    31:3   error    'module' is not defined                       no-undef

[atoppi]

@redexp yeah, please fix those and also the issues about indentation.
If you wanna test locally before triggering our github workflow, just use eslint janus.js with our eslint configuration file (.eslintrc.js).