index.ts

// Declaring object with custom type
let user:{id:number,name:string,email:string} = {
  id:10,
  name:'Rahul',
  email:'a@g.com'
}
console.log(user.id)
// 10

console.log(user.number)
// error TS2339: Property 'number' does not exist on type '{ id: number; name: string; email: string; }'.

user.age = 10 
console.log(user.age)
// error TS2339: Property 'age' does not exist on type '{ id: number; name: string; email: string; }'.