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A.5. Arrow function expressions

Arrow function expressions (a.k.a. fat arrow functions) provide a shorter notation for anonymous functions and add lexical scope for the this variable. The syntax of arrow function expressions consists of arguments, the fat arrow sign (=>), and the function body. If the function body is just one expression, you don’t even need curly braces. If a single-expression function returns a value, there’s no need to write the return statement—the result is returned implicitly:

let sum = (arg1, arg2) => arg1 + arg2;

The body of a multiline arrow function expression has to be enclosed in curly braces and use the explicit return statement:

(arg1, arg2) => {
  // do something
  return someResult;
}

If an arrow function doesn’t ...