Rule proposal: `no-typeof-undefined`

Less code written

Fail

typeof foo === 'undefined'

Pass

foo === undefined

[fisker]

I don’t think no-undef is safe, for example, when you write code for browser, the following won’t report, because AbortController is considered “defined” as globals.

if (AbortController !== undefined) {}

But when you run this code in old browsers don’t support AbortController , it will throw.

if (typeof AbortController !== 'undefined') {}

This won’t.

Of cause, 'AbortController' in globalThis or globalThis.AbortController are safer. But nothing wrong to use typeof.

[fisker]

When it’s undefined variable, foo === undefiend will throw

foo === undefined
VM227:1 Uncaught ReferenceError: foo is not defined
    at <anonymous>:1:1