The reference passed into parse gets mutated, which is unexpected (especially when you, like I, use a file-level constant as the reference).

> options = {}
{}
> qs.parse('', options);
{}
> options
{"delimiter":"&","depth":5,"arrayLimit":20,"parseArrays":true,"allowDots":false,"plainObjects":false,"allowPrototypes":false,"parameterLimit":1000,"strictNullHandling":false}

The same is true of stringify, but to a lesser degree.

Neither parse nor stringify should modify any of their input parameters.