Functions using arrow function Expression

var multiply = function (num: number) {
        return num * num;
}

The same above function could be written using arrow key expression as below

var multiply = (num1: number, num2: number) => return num1 * num2;

//With flower braces in case of multiple statements
var multiply = (num1: number, num2: number) => {return num1 * num2;};

we can also do function declaration and definition in two separate lines as one below

//function declaration
var multiply: (num1: number, num2: number) => number;    

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

//function taking object literals as arguments
var multiply: (numbs: { num1: number, num2: number }) => number;    
var numbs = { num1: 2, num2: 4 };

multiply = function (numbs) {
   return numbs.num1 * numbs.num2;
}