In bug 1813517 I added another case where we take an attributes property to set arbitrary attributes on an element. We should consolidate and share this code with other places doing the same thing, thereby fixing a few shortcomings:

• properly set boolean attributes as foo=""/[attribute absent] instead of foo="true"/foo="false"
• avoid creating and iterating over a dummy object in case the attribute property isn't set
• don't override previously set-via-classList classes when setting the class attribute
• remove the attribute when the value is undefined (current === null check is too strict)

In bug 1813517 I added another case where we take an attributes property to set arbitrary attributes on an element. We should consolidate and share this code with other places doing the same thing, thereby fixing a few shortcomings:

• properly set boolean attributes as foo=""/[attribute absent] instead of foo="true"/foo="false"
• avoid creating and iterating over a dummy object in case the attribute property isn't set
• don't override previously set-via-classList classes when setting the class attribute
• remove the attribute when the value is undefined (current === null check is too strict)

https://hg.mozilla.org/mozilla-central/rev/e37f5cc3f9e9