max-depth

To understand a line that sits five blocks deep, you have to keep every condition and loop around it in your head. This rule reports any statement nested deeper than the maximum, which is 4 by default.

if, switch, try, for, while, do and with each add one level. Every function starts again at zero.

Configure

Off by default. To turn it on:

[lint.rules]
"max-depth" = "error" # or "warn"

Every option, set to its default. The ones that are commented out are unset by default.

[lint.rules]
"max-depth" = ["error", {
  max = 4,
  # maximum = <number>,
}]

Examples

With a maximum of 2, this is reported:

function notify(users) {
  for (const user of users) {
    if (user.active) {
      if (user.email) {
        send(user.email);
      }
    }
  }
}

Not reported:

function notify(users) {
  for (const user of users) {
    if (user.active && user.email) {
      send(user.email);
    }
  }
}

An else if is as deep as the if it continues. This passes with a maximum of 1:

if (size < 10) {
  small();
} else if (size < 100) {
  medium();
} else {
  large();
}

So does this, because the inner if is the first level of the callback:

if (ready) {
  items.forEach((item) => {
    if (item.done) {
      archive(item);
    }
  });
}

Options

[lint.rules]
max-depth = ["error", 3]

Option	Default	What it does
max	4	The deepest level allowed. maximum is an older name for it.

A number alone is short for { "max": number }.