Function

• Similar to JavaScript functions

• Have some additional features...

  • types

  • default parameters

  • rest parameters

  • lambdas

function greet(){
    alert("Hello world.");
}

Function Types

• Functions can have types

• Types describe what is returned by a function

function getCountry() : string {
    return "Canada";
}
var c : string = getCountry(); // ok
var c : number = getCountry(); // compile-time error

Optional Parameters

function sayHappyBirthday(name?: string){
    console.log("Happy Birthday " + name);
}

sayHappyBirthday(); // OK
sayHappyBirthday("Hemant"); // OK

Default Parameters

function sayHappyBirthday(name?: string = "Buddy!"){
    console.log("Happy Birthday " + name);
}

sayHappyBirthday(); // Happy Birthday Buddy!
sayHappyBirthday("Hemant"); // Happy Birthday Hemant

Rest Parameters

• In JavaScript list of all arguments are provided in the mysterious arguments variable

• it's real array ( so we can use array methods push, pop etc on it unlike arguments )

function roleCall(master: string, ...names : string[]){
    console.log("Master is "+ master); // Master is Hemant
    console.log(names);  // ["Rickon", "Sansa", "Robb", "Arya"]
};
roleCall("Hemant","Varun","Vinay","Sasis","Arya");

Lambdas ( arrow function )

• A different kind of function invocation where the value of this is not changed

• Works similar to function but has a preferable syntax

• Also known as an arrow or a fat arrow function

var superhero = {
    name: "Hemant",
    greet: function() {
        setTimeout(() => {
            console.log(this.name); // Hemant
        }, 500);
    }
};

superhero.greet();