Mastering JavaScript Functional Programming

Returning values

In lambda style, functions only consist of a result. For the sake of brevity, the new arrow functions provide a syntax for this. When you write something like (x,y,z) => followed by an expression, a return is implied. For instance, the following two functions actually do the same as the sum3() function we showed previously:

const f1 = (x, y, z) => x + y + z;const f2 = (x, y, z) => {    return x + y + z;};

If you want to return an object, then you must use parentheses, or otherwise, JS will assume code is meant. 

"A matter of style: when you define an arrow function with only one parameter, you can omit the parentheses around it. For consistency, I prefer always including them. However, the formatting tool I use, prettier, doesn't ...