for-direction

A loop that tests i < 10 and then runs i-- moves away from 10, so the test stays true and the loop never ends. It's almost always a typo, like -- for ++ or < for >.

The rule looks at ++, --, += and -= on the counter. If it can't tell whether the step is positive or negative, it reports nothing.

This rule is on by default.

Configure

On by default as an error. To turn it off:

[lint.rules]
"for-direction" = "off" # or "warn"

Examples

Reported:

for (let i = 0; i < items.length; i--) {
  render(items[i]);
}

for (let i = items.length - 1; i >= 0; i += 1) {
  render(items[i]);
}

Not reported:

for (let i = 0; i < items.length; i++) {
  render(items[i]);
}

for (let i = items.length - 1; i >= 0; i -= 1) {
  render(items[i]);
}

The rule can't know the sign of step here, so it leaves the loop alone:

function walk(items, step) {
  for (let i = 0; i < items.length; i += step) {
    render(items[i]);
  }
}