2. JavaScript Variables

2.2. Using let


          let variables are declared in a similar manner to var declared variables. When we use the let keyword rather than var; it imposes scope constraints. The let declared variables cannot be redeclared. This will give you a SyntaxError if you will try to do so. The scope of those variables is the block they are defined in, also in any sub-blocks. The browser will throw a ReferenceError if you are trying to access these variables outside of their block.

let x; // without initializing 

let x = 5; // initialize with a number.