Passing an undefined query param can prevent the url from updating

[cvn]

Version

3.0.2

Reproduction link

https://plnkr.co/edit/yJJpcKuhYQwdOk3nZcZs?p=preview

Steps to reproduce

1. Start with the url /?q=foo&color=bar.
2. this.$router.push({query: {q: 'foo', offset: undefined}})

What is expected?

I expect the url to change to /?q=foo

What is actually happening?

The url does not change

---

I'm doing search filtering using query params. Every time I change a filter, I
add/remove/modify the appropriate param, and reset my pagination by setting
an offset param to undefined. In my app, the combination of removing a param
and offset not being set to begin with, causes the route not to update.

This issue is easy enough to work around, but it took me a while to figure out
what was going on.

[posva]

For the moment the way to do it is to remove the property from the object (instead of providing undefined). The thing is it is kept in $route.query which shouldn't in order to be consistent when coming directly by entering the url

Technically, removing the query parameters would be a breaking change so I will keep this open for next major version

[cvn]

@posva To be clear, using undefined to remove a query parameter already works:

1. Start with /?q=foo
2. this.$router.push({query: {q: undefined}})
3. The url changes to /

Using undefined only fails in some circumstances.

[posva]

I'm talking about this, these are how the tests should be written: undefined values should be removed from resulting query object

 it('should work consistently', () => {
    router.push({ query: { bar: 'bar' } })
    router.push({ query: { bar: undefined } })
    expect(location.hash).toEqual('#/')
    expect(router.app.$route.query).toEqual({ })
  })
it('should support the example use case', () => {
    router.push({ query: { q: 'foo', color: 'bar' } })
    router.push({ query: { q: 'foo', color: undefined } })
    expect(location.hash).toEqual('#/?q=foo')
    expect(router.app.$route.query).toEqual({ q: 'foo' })
  })

Technically it would be a breaking change

[posva]

Closing as this was fixed in v4