Basics of Typescript

Variables

• let: Declares a block-scoped variable. Can be reassigned.

  let username = 2;
  // username = "Rohit"; // Not allowed

• const: Declares a block-scoped constant. Cannot be reassigned.

  const age = 25; // Constant variable

Literal Types

• Define a type based on a specific value.

  let humidity: 79 = 79;
  humidity = 79; // Allowed
  // humidity = 78; // Not allowed
  
  let x = 10 as 79; // Type assertion (not recommended)
  console.log(x);

Type Casting

• Explicitly change the type of a variable.

  let y = new Date();
  let y2 = y as any; // Type casting

Function Typing

• Specify the types of parameters and the return type.

  const add = (a: number, b: number): number => {
    return a + b;
  };
  // const result = add(2, "3"); // Error
  // new Promise(result); // Error

Tips

1. Always be explicit about function return types.
2. Catch errors at function declaration for better maintainability.

Key Concepts

• TypeScript helps catch errors at compile time.
• Literal types enforce strict value assignment.
• Type casting should be used judiciously.
• Clear function typing improves code readability and maintainability.