Return Early

A pattern you will see with many of the functional programming principles is to return early from a function. This pattern can be seen with early return, guard clauses, and continue statements.

Early Return

Early return, as the name suggests, is a pattern where you check for certain conditions and return from the function early. Take the following example:

function isBigEnough(number) {
  if (number >= 10) {
    return true;
  } else {
    return false;
  }
}

This function can be refactored to:

function isBigEnough(number) {
  return number >= 10;
}

Guard Clauses

Guard clauses are similar to early returns, but are used to check for invalid input. A guard clause is placed at the start of a function, and if the input does not meet the criteria, it will return early.

function withdraw(amount) {
  if (amount > account.balance) {
    return;
  }
 
  account.balance -= amount;
  return amount;
}

Continue

The continue statement can be used to return early from a loop. It will skip the rest of the loop and continue with the next iteration.

for (let i = 0; i < 10; i++) {
  if (i % 2 === 0) {
    continue;
  }
 
  console.log(i);
}