Javescript variable declaration -- VaR, let, const

keyword	var	let	const
attribute 1	Declare as a global variable in the global	Declare as a global variable in the global , But it can't be used. window Object access	Same as let
attribute 2	Declare a local variable inside a function	Block variable	Same as let
attribute 3	Variable promotion	There is a temporary dead zone	Same as let
attribute 4	Can be redundant declaration	Repeated declaration of the same variable will report an error	Same as let
attribute 5	Can be changed at will	Can be changed at will	It cannot be changed at will , But you can change the reference type variable