JavaScript Arrow Function

There is another simplified way to declare a function, which is often better than Function Expression known as 'Arrow functions'

function sum(a, b) {
    return a + b;
};
alert( sum(1, 2) ); // 3

let sum = function(a, b) {
    return a + b;
};
alert( sum(1, 2) ); // 3

let sum = (a, b) => a + b;


alert( sum(1, 2) ); // 3

If we have only one argument, then parentheses around parameters can be omitted, to make it shorter.

let square = n => n * n;
alert( square(5) ); // 25

If there are no arguments, parentheses are empty, but they must be present:

let hello = () => alert('Hello!');
hello();

Arrow functions can be used in the same way as Function Expressions.

let age = prompt("Enter your age?");
let checkAge = (age < 18) ?
  () => alert('Young') :
  () => alert('Adult');
checkAge();

Sometimes we need a more complex function, with multiple expressions and statements. In that case, we can enclose function statements in curly braces. The major difference is that curly braces requires a return keyword to return a value

let sum = (a, b) => a + b;
// "return" is not required
alert( sum(1, 2) ); // 3

let sum = (a, b) => {
    let result = a + b;
    return result; 
//if curly braces used, then 'return' is required
};
alert( sum(1, 2) ); // 3