Mastering JavaScript Functional Programming - Second Edition

Returning values

In the lambda coding 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 that 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; otherwise, JavaScript will assume that code follows. 

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 to always include them. However, Prettier, the ...