Version

2.6.11

Reproduction link

https://jsfiddle.net/0jh1psog/

Steps to reproduce

Open the console in the provided JSFiddle
or
run Vue.config.getTagNamespace('foreignObject')

What is expected?

Vue.config.getTagNamespace('foreignObject') should return 'svg'

What is actually happening?

It returns undefined.

This causes a warning Unknown custom element: <foreignObject> when testing such components using vue-test-utils

---

This is caused by

It should be foreignobject with lowercase o here, because of the makeMap implementation.

To avoid such bugs in the future, even better fix:

should be map[expectsLowerCase ? list[i].toLowerCase() : list[i]] = true