1;
let names = ["Mario", "Marian", "David"];
names.push("Heath");
names.push(22); // Not allowed

2;
let names = ["Mario", 33, "David", 91];
names.push("Heath");
names.push(22); // Allowed
names.push(true); // Allowed
names[1] = 123; // Allowed

names = "String"; // names is an array. Its type can't be changed.

   1.
   let ninja = {
     name: 'mario',
     belt: 'black',
     age: 22
   }

   ninja.age = 33;
   ninja.name = "David"
   ninja.age = "24" // Not allowed - change property type not possible.
   ninja.skills:['Fighting'] // Not allowed - adding addtional property not allowed

let name: string;
let age: number;
let isLoggedIn: boolean;

let ninjas: string[] = []; // we need to initalize ninjas with value of empty array otherwise it won't work.
ninjas.push("David"); // It will work perfectly fine.

let ninjas2: sting[];
ninjas.push("David"); // It will throw err - Cannot read property 'push' of undefined.

let mixedArray: (string | numbers)[] = [];
mixedArray.push(22);
mixedArray.push("David");

let uID: string | number;

let ninjaObject: object;
ninjaObject = { name: "Test", age: 22 };
ninjaObject = []; // it can hold value of array as Array is a kind object.

let ninjaObject2: {
  name: string,
  age: number,
};
// ninjaObject2 will only take two above defined property.

let age: any = 22;
age = true; // changed type to boolean but no error.
age = { name: "Test" }; // changed type to Object but no error.

  tsc --init // initializes typescript configuration
  tsc // Generate javascript file equivalent to typescript file. Source & output must be configured inside tsconfig.json
  tsc -w // Will watch the changes & run automatically

  "outdir": "./public", // All output JS files will be saved here in public folder.
  "rootdir":"./src" // source Files will pciked from src folder
  "include": ["src"] // typescript will consider src folder as a input.

const add = (a: number, b: number, c?: number | string) => {
  console.log(a + b);
  // value of c will be undefined if not being passed
};
add(3, 4); // we are not passing third arguments as it is optional. '?' is used for adding optional property.

// Using Default value
const add = (a: number, b: number, c: number | string = 10) => {
  console.log(a + b + c);
  // Here we are not using optional property "?" as we are already providing default value.
};
add(3, 4); // If we pass any value for third argument, it will override it.

// Return type of a function.
const add(a:number):number{
  return a+3;
}
// If it doesn't return anyvalue, we could use "void".

let calc = (num1: number, num2: number) => number;

calc = (numOne: number, numTwo:number) =>{
  return numOne+numTwo;
}
---------------------
type Person = {
  name: string,
  age: number
}

let logDetails:(obj: Person) => void;
logDetails = (ninja: Person) => {
  console.log(ninja.name)l
}