12. jquery source code parsing. EQ (). First (). Last (). Slice ()

EQ (Index): Extracts the elements in the collection that are indexed as index.
First (): Returns an element in the collection.
. Last (): Protect the final element in the collection.
. Slice (Start[,end]): Returns the element of a given interval segment in the collection.
First () and last () call EQ (), EQ () is implemented through slice (), slice () through
. Pushstack () implementation.
Related source

285 line: The usage is peculiar, by a "+" to convert the possible string I to a numeric value.
300~301: First borrow array method slice () get a subset of the specified range from the current jquery object,
Span style= "font-family: italics; font-size:18px; " > in the drop-down method Pushstack () converts a subset to a jquery object, while retaining a reference to the current jquery object through the property prevobject.