Variable operation

1. What is the purpose of variables ？

   • Store the data
   • For the beauty of the code

2. let and const The difference between declared variables is ：

   let Declared variables can be left unassigned ,const The declared variable must be assigned , Otherwise, the report will be wrong 
   

3. let The correct result of repeating the declaration of variables is ？

   • Overwrite the original value
   • Report errors
   • No impact
   • Both values are saved in variables

4. What is constant ？ A constant quantity __

5. After the following code is run , The right result is ？

   const a;
   const b = 2;
   a = 1;
   console.log(a + b);
   

   • Output 3
   • Report errors
   • Output 2
   • Output 4

6. In what situation does the following sentence appear

   a is not defined

   • Use an undeclared variable a
   • Variable a Incorrect declaration command used when declaring
   • Declare variables a There is no ending sign when writing
   • Variable a Not used after declaration

7. Variables should be used before they are declared

   • Yes
   • incorrect

8. Which of the following are the correct keywords for declaring variables ？

   • let
   • const
   • var
   • int

9. Which of the following symbols are JS Annotators in

   • //
   • /**/
   • <！-- -- >
   • #