es6 of let

es5 provides two ways of declaring variables

　　the function

es6 in offers four ways to declare variables

　　let　　const　　class　　import

Note: Do not ignore the private variable function parameter function;

var define the variable

　　var features: variable lift but not defined, add a property to provide window

function defined variables

　　function features: either upgrade also defined variables.

let define the variable

　　1. There is no variable enhance the function can not be used before it is declared;

　　

　　 

　　2. The statement can not be repeated

　　

 

　　3. not add properties to the window