Parameter In Typescript

In Typescript, function parameters allow us to pass values into a function when it is called.

Parameters help define the inputs that a function expects, and we can specify their types to ensure type safety.

Parameter Syntax:

function multiple(num1: number, num2: number): number {
  return num1 * num2;
}

Note: "num1" and "num2" are parameters of the function add. They are annotated with their types (number), indicating that the function expects two numeric parameters.

Optional Parameters:

We can make parameters optional by adding a "?" after their key-name.

Example:

function invoice(message: string, name?: string ): string {
  if (name) {
    return `Hi ${name}!, ${message}, `;
  } else {
    return `Hello, ${message}!`;
  }
}

const result1 = invoice("Thank u for renew subscription")
console.log(result1) // Output: "Hello, Thank u for renew subscription!" 


const result2 = invoice("Thank u for renew subscription", "Alice")
console.log(result2) // Output: "Hi Alice!, Thank u for renew subscription, "

Note: "name" parameter is optional. We can call the function with one or two arguments.

Default Parameters:

Example:

function multiply(num1: number, num2: number = 5): number {
  return num1 * num2;
}

// passing only one argument
const result1 = multiply(10)
console.log(result1) // Output: 50

// passing two argument
const result2 = multiply(10, 20)
console.log(result2) // Output: 200

We can provide default values for parameters.

Note: if the `num2` parameter is not provided, it defaults to 2.

Example:

function sum(...numbers: number[]): number {
  return numbers.reduce((acc, val) => acc + val, 0);
}


const result: number = sum(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
console.log(result) // Output: 55

Rest Parameters:

We can use the rest parameter syntax (...) to represent an indefinite number of parameters as an array.

Example:

function printEmployee(name: string, deptNo: number): void {
  console.log(`Name: ${name}, DepartmentNo: ${deptNo}`);
}

// Output: "Name: Alice, DepartmentNo: 1002" 
printEmployee("Alice", 1002 )

Note: The numbers parameter captures any number of arguments as an array.

Parameter Types:

Example:

function printStatusCodeWithMessage({ code, message }: { code: number, message: string }): void {
  console.log(`Response: statusCode=${code}, message=${message}`);
  // Output: "Response: statusCode=200, message=Success" 
  // Output: "Response: statusCode=404, message=Page not found" 
}

printStatusCodeWithMessage({code: 200, message: "Success"});
printStatusCodeWithMessage({code: 404, message: "Page not found"})

We can specify the types of parameters to ensure type safety.

Note: "name" must be a string, and "deptNo" must be a number.

Parameter Destructuring:

We can use parameter destructuring to simplify the handling of complex objects.

Note: This function expects an object with `code` and `message` properties.

<-- Function vs Arrow Function

Classes -->

Parameter In Typescript

In Typescript, function parameters allow us to pass values into a function when it is called.

Parameters help define the inputs that a function expects, and we can specify their types to ensure type safety.

Parameter Syntax:

function multiple(num1: number, num2: number): number {
  return num1 * num2;
}

Note: "num1" and "num2" are parameters of the function add. They are annotated with their types (number), indicating that the function expects two numeric parameters.

Optional Parameters:

We can make parameters optional by adding a "?" after their key-name.

Example:

function invoice(message: string, name?: string ): string {
  if (name) {
    return `Hi ${name}!, ${message}, `;
  } else {
    return `Hello, ${message}!`;
  }
}

const result1 = invoice("Thank u for renew subscription")
console.log(result1) // Output: "Hello, Thank u for renew subscription!" 


const result2 = invoice("Thank u for renew subscription", "Alice")
console.log(result2) // Output: "Hi Alice!, Thank u for renew subscription, "

Note: "name" parameter is optional. We can call the function with one or two arguments.

Default Parameters:

Example:

function multiply(num1: number, num2: number = 5): number {
  return num1 * num2;
}

// passing only one argument
const result1 = multiply(10)
console.log(result1) // Output: 50

// passing two argument
const result2 = multiply(10, 20)
console.log(result2) // Output: 200

We can provide default values for parameters.

Note: if the `num2` parameter is not provided, it defaults to 2.

Example:

function sum(...numbers: number[]): number {
  return numbers.reduce((acc, val) => acc + val, 0);
}


const result: number = sum(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
console.log(result) // Output: 55

Rest Parameters:

We can use the rest parameter syntax (...) to represent an indefinite number of parameters as an array.

Example:

function printEmployee(name: string, deptNo: number): void {
  console.log(`Name: ${name}, DepartmentNo: ${deptNo}`);
}

// Output: "Name: Alice, DepartmentNo: 1002" 
printEmployee("Alice", 1002 )

Note: The numbers parameter captures any number of arguments as an array.

Parameter Types:

Example:

function printStatusCodeWithMessage({ code, message }: { code: number, message: string }): void {
  console.log(`Response: statusCode=${code}, message=${message}`);
  // Output: "Response: statusCode=200, message=Success" 
  // Output: "Response: statusCode=404, message=Page not found" 
}

printStatusCodeWithMessage({code: 200, message: "Success"});
printStatusCodeWithMessage({code: 404, message: "Page not found"})

We can specify the types of parameters to ensure type safety.

Note: "name" must be a string, and "deptNo" must be a number.

Parameter Destructuring:

We can use parameter destructuring to simplify the handling of complex objects.

Note: This function expects an object with `code` and `message` properties.

<-- Function vs Arrow Function

Classes -->