ionic \ angular 2：settimeout后字符串不会更新

I'm trying to update a string (of a class\tag) with settimeout (or any other callback), with no success, It's working perfectly with a button (when the user is clicking the button to update), but it doesn't work with JS settimeout. can you tell me what am I missing here?I'm trying to update a string (of a class\tag)