const-array-object.js

// declare an array with const
const arr = [1, 2, 3];
console.log(arr) // [1, 2, 3]

// try to re-decalre an array with the same name and cought an error
let arr = [2, 3, 4]; // SyntaxError: Identifier 'arr' has already been declared

// but you can change the value
arr.push(4);
console.log(arr); // [1, 2, 3, 4]

// declare an object
const myObj = {
  firstName: 'Jamal',
  lastName: 'Uddin'
};

// can't re-declare any object with same name when used const
const myObj = { age: 23 }; // SyntaxError: Identifier 'myObj' has already been declared

// but you can change the key and values
myObj.age = 23;
console.log(myObj); // {firstName: "Jamal", lastName: "Uddin", age: 23}
myObj.message = () => `Hello! I am ${this.firstName} ${this.lastName}, I am ${this.age} years old young man! learning JavaScript & React.`;
console.log(myObj.message()); 
// Hello! I am undefined undefined, I am undefined years old young man! learning JavaScript & React.