{"action":"closed","issue":{"url":"https://api.github.com/repos/whatwg/dom/issues/332","repository_url":"https://api.github.com/repos/whatwg/dom","labels_url":"https://api.github.com/repos/whatwg/dom/issues/332/labels{/name}","comments_url":"https://api.github.com/repos/whatwg/dom/issues/332/comments","events_url":"https://api.github.com/repos/whatwg/dom/issues/332/events","html_url":"https://github.com/whatwg/dom/issues/332","id":178690609,"number":332,"title":"Why is the second parameter to MutationObserver.observe() optional?","user":{"login":"cdumez","id":995975,"avatar_url":"https://avatars.githubusercontent.com/u/995975?v=3","gravatar_id":"","url":"https://api.github.com/users/cdumez","html_url":"https://github.com/cdumez","followers_url":"https://api.github.com/users/cdumez/followers","following_url":"https://api.github.com/users/cdumez/following{/other_user}","gists_url":"https://api.github.com/users/cdumez/gists{/gist_id}","starred_url":"https://api.github.com/users/cdumez/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/cdumez/subscriptions","organizations_url":"https://api.github.com/users/cdumez/orgs","repos_url":"https://api.github.com/users/cdumez/repos","events_url":"https://api.github.com/users/cdumez/events{/privacy}","received_events_url":"https://api.github.com/users/cdumez/received_events","type":"User","site_admin":false},"labels":[],"state":"closed","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":1,"created_at":"2016-09-22T18:49:37Z","updated_at":"2016-09-23T06:52:08Z","closed_at":"2016-09-23T06:52:08Z","body":"The second parameter to MutationObserver.observe() is optional in the specification. I don't understand why we don't simply mark it as mandatory considering that it will throw a TypeError if omitted anyway.\r\n\r\nBehavior of browser engines:\r\n- Gecko agrees with the spec (Argument is optional but throws a TypeError when omitted)\r\n- WebKit / Blink mark the second parameter as mandatory"}}
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