Visual mnemonic for an array sorter's return values

Published on in JavaScript and Mnemonics

When sorting an array with a custom comparator function, the function should return <0, 0 or >0. But what do the values do? Use this weird visual mnemonic – sorting consultants HATE it!

First, recall that an array sorter compares two values, a and b:

array.sort((a, b) => {
  // ...

Second, because the sorter function should return a number, imagine an x-axis with the numbers -1, 0 and +1:

An x-axis with -1, 0 and +1.

Now, realize that -1 is on the left side of the x-axis, and +1 is on the right side:

  • Returning -1 (or anything less than zero) from the array sorter moves a to the left (before b in the array).
  • Returning +1 (or anything greater than zero) from the array sorter moves a to the right (after b in the array).
  • (Returning 0 keeps the order of a and b.)

And why is a moved relative to b – because the array sorter compares two values (a and b), and a comes first in the function parameters ((a, b) => {}). First come, first served.

Like so:

An x-axis visualizing that when comparing values  and , returning -1 moves  to the left, and returning +1 moves  to the right.

That's it! To recap:

array.sort((a, b) => {
  return -1 // <-a
  return +1 //   a->
  return 0 // Keep order of `a` and `b`

(Illustrations mouse-drawn on