env-builtin.md

builtin env

By default, every native JavaScript global, and some very common ones (such as setTimeout) have been set as globals. The full list is here.

Example:

Good

setTimeout(fn, 0);
new Promise();

Ok, but not preferred

window.setTimeout(fn, 0);
// Ugh... this is just awful.
var globalObject = typeof window === 'undefined' ? typeof global === 'undefined' ? self : global : window;
new globalObject.Promise();

Justification

Every one of these variables is expected to be available on every browser and Node.js - in other words, pretty much every environment a typical JavaScript developer would work in. Trying to refer to these off of the global object can be a pain, as the global object is sometimes called window (e.g. in a browser), sometimes global (e.g. node.js) and sometimes self (e.g. in a web worker or service worker), and so having to shim a global variable just to use a Promise or Array would be a big pain.

How to disable

If you don't want to set these variables as global, you can simply set the builtin env to false in your project config:

package.json (project-wide)

"eslintConfig": {
  "extends": ["strict/es5"],
  "env": {
    "builtin": false
  }
}

If you have a particular file you know you won't be using them for, you customise what envs you use by changing the eslint-env setting, from within a file:

*.js (file wide)

/*eslint-env node */ // < list all environments this file needs