jQuery Useful Functions

each()
Is a generic iterator function, which can be used with objects and arrays.
each vs for loop, $.each vs $().each vs for

map()
Returns a new array with changes applied
Difference between map and each

extend()
Merges two or more objects into to the first object and returns it.

data()
data

inArray()
Checks if an item is in array

noop()
declares an empty function. Rather than passing an anonymous functions you can use this.

proxy()
Takes a function and returns a function which will always have a particular context.