How important is mathematical logic and set theory in mathematics? I'm talking about topics such as model theory, proof theory, predicate calculus, Godel's incompleteness, ordinal numbers, large cardinals, etc. How much of these do I need to know if I want to specialize in some other areas of mathematics such as algebra and topology?
How much set theory and logic should typical algebraists/analysts/geometers know? (soft-question) I know enough amount of set theory and logic to study grad-level math. However, I don't know more advanced set theory and logic, such as the ones on Kunen's or Shoenfield's texts. Although it's good to learn such advanced topics, I may not have enough time to do so, since I will probably put my emphasis on algebra, analysis or geometry as well as mathematical physics.   Although how much set theory and logic I should learn is totally up to what sort of analysis, algebra or geometry I will study, I want to know how much of them typical competitive algebraists/analysts/geometers know. If you are one of them, how much do you know?
How do JavaScript closures work? How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?  I have seen  given on Wikipedia, but unfortunately it did not help.