My least favorite is assign.
Not only does JavaScript feature that natively (though I suppose the library may predate widespread support for Object.assign), the 1-liner assign flips the order of the parameters!
assign({ a: true }, { a: false }) -> { a: true }
Object.assign({ a: true }, { a: false }) -> { a: false }
And most of them are just straight-up pointless! Like, let's introduce a dependency for decrement lolEDIT: In looking up whether the 1-liners assign predated widespread Object.assign support, I found that their implementation - confusingly named extend[1] at first - literally used Object.assign from the very beginning. And they still chose to mess with the parameter order. For shame lol
[0] https://github.com/1-liners/1-liners
[1] https://github.com/1-liners/1-liners/blob/7c1f8d51df4b4b3e0a...