Using Boolean prefixes for variables

Prefixes like “is”, “has”, or “does” help emphasize that a variable holds a Boolean value.

if (monday) {
  // `monday` could be the date of next Monday. You wouldn’t expect this to
  // be `true` or `false`.

if (isMonday) {
  // This reads like the question “is Monday?”, which you would answer with
  // “yes” or “no”. The name tells you that this has to be Boolean.

if (children) {
  // `children` could be a list of names or whether a person has children or
  // not. It’s difficult to tell if this is an array or a Boolean.

if (hasChildren) {
  // You can only read this as “has children?”, which is either `true` or
  // `false`. Ideally.

if (rocks) {
  // Could be the name of your favorite rocks, like “The” or “30”.

if (doesRock) {
  // This does rock, `true`. Note how it’s not called `doesRocks`, which
  // would read a little awkward.