@typescript-eslint/prefer-includes

tags.indexOf("draft") !== -1 gets a position and compares it with a magic number, only to find out if the value is there. It's easy to write > 0 instead of >= 0 and miss the first element. tags.includes("draft") asks the question directly.

The rule works for strings, arrays, and any of your own types that has an includes method with the same parameters as its indexOf. It also reports .test() on a regular expression that only matches one fixed string, such as /admin/.

--fix rewrites both forms. tags?.indexOf("draft") !== -1 is reported but not fixed.

Configure#

Off by default. This rule needs types, so turning it on makes bun lint type check your code first.

[lint.rules]
"@typescript-eslint/prefer-includes" = "error" # or "warn"

Examples#

function check(tags: string[], path: string) {
  if (tags.indexOf("draft") !== -1) return false;
  if (path.indexOf("/private/") >= 0) return false;
  return /admin/.test(path);
}

function check(tags: string[], path: string) {
  if (tags.includes("draft")) return false;
  if (path.includes("/private/")) return false;
  return path.includes("admin");
}

Code that uses the position, or a regular expression that does more than match a fixed string, is left alone:

function slice(path: string) {
  const start = path.indexOf("/private/");
  if (/^admin/.test(path) || /admin/i.test(path)) return "";
  return path.slice(start);
}

A type that has no includes method is left alone too:

interface Playlist {
  indexOf(song: string): number;
}

function has(playlist: Playlist, song: string) {
  return playlist.indexOf(song) !== -1;
}