const

// :        ,
//     .      
//  .

//  MY_FAV       7
const MY_FAV = 7;

//     - Uncaught TypeError: Assignment to constant variable.
MY_FAV = 20;

//  7
console.log("my favorite number is: " + MY_FAV);

//   ,    - Uncaught SyntaxError: Identifier 'MY_FAV' has already been declared
const MY_FAV = 20;

//  MY_FAV   ,  
//  
var MY_FAV = 20;

//    
let MY_FAV = 20;

//       
if (MY_FAV === 7) {
  //  .     MY_FAV .
  // (     let     ,   const)
  const MY_FAV = 20;

  // MY_FAV  20
  console.log("my favorite number is " + MY_FAV);

  //        
  var MY_FAV = 20;
}

// MY_FAV     7
console.log("my favorite number is " + MY_FAV);

//  ,      - Uncaught SyntaxError: Missing initializer in const declaration
const FOO;

// const    
const MY_OBJECT = { key: "value" };

//        - Uncaught TypeError: Assignment to constant variable.
MY_OBJECT = { OTHER_KEY: "value" };

// ,   ()  
MY_OBJECT.key = "otherValue"; //  Object.freeze()  ,    

//      
const MY_ARRAY = [];
// ,     
MY_ARRAY.push("A"); // ["A"]
//       .    - Uncaught TypeError: Assignment to constant variable
MY_ARRAY = ["B"];