Arrow functions

Arrow functions creates a function that accepts arguments arg1..argN, then evaluates the expression on the right side with their use and returns its result.
```
let func = (arg1, arg2, ..., argN) => expression;
```

In other words, it’s the shorter version of:

let func = function(arg1, arg2, ..., argN) {
  return expression;
};

If the function only has one line in the curly brackets, you can omit the curly brackets {}.
If the function only takes one parameter, you can also omit the brackets around the parameter ().

If your function needs to return a value, and contains only one line, you can also omit the return statement.

let age = prompt("What is your age?", 18);

let welcome = (age < 18) ?
	() => alert('Hello!') :
	() => alert("Greetings!");

welcome();

For multiline arrow functions:

let sum = (a, b) => {  // the curly brace opens a multiline function
  let result = a + b;
  return result; // if we use curly braces, then we need an explicit "return"
};

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