What is the license for this plugin?
If there was a license for this plugin, it would have been mentioned in the readme or in a separate file. So far I don't think there is a license for it.
The source code of the current master branch (https://github.com/aarondo/Strength.js/blob/a80499ea7a31032598e478be7853c5861b0e10a0/src/strength.js#L5) says it's MIT-licensed. I'd argue it would be preferable to have the license within the repository, though.
Gotcha, thanks for clearing that up. I would agree that the license should be posted somewhere more obvious. Having it stashed in one of the source files probably isn't the best way to go. Most projects put it in the repo's README.md file and/or in an appropriately named file in the root of the repo.