JS Fundamentals - Functions

Question 1

Function Declaration

Answer 1

function showMessage() {
  alert( 'Hello everyone!' );
}

Question 2

function without a return statement

Answer 2

function checkAge(age) {
  if (age >= 18) {
    return true;
  } else {
    return confirm('Do you have permission from your parents?');
  }
}

It is possible to use return without a value. That causes the function to exit immediately.

For example:

function showMovie(age) {
  if ( !checkAge(age) ) {
    return;
  }

Question 3

returns undefined

Answer 3

If a function does not return a value, it is the same as if it returns undefined:

function doNothing() { /* empty */ }

alert( doNothing() === undefined ); // true

Question 4

An empty return is also the same as return undefined

Answer 4

function doNothing() {
  return;
}

alert( doNothing() === undefined ); // true

Question 5

Never add a newline between return and the value

Answer 5

For a long expression in return, it might be tempting to put it on a separate line, like this:

return
(some + long + expression + or + whatever * f(a) + f(b))
That doesn’t work, because JavaScript assumes a semicolon after return. That’ll work the same as:

return;
(some + long + expression + or + whatever * f(a) + f(b))
So, it effectively becomes an empty return.

Question 6

Solution

Answer 6

If we want the returned expression to wrap across multiple lines, we should start it at the same line as return. Or at least put the opening parentheses there as follows:

return (
  some + long + expression
  \+ or +
  whatever * f(a) + f(b)
  )