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Add historical note to no-typeof-undefined #1992

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merged 4 commits into from Dec 3, 2022
Merged

Add historical note to no-typeof-undefined #1992

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811e0b4
Add historical note to `no-typeof-undefined`
fregante Nov 27, 2022
342a79a
accidentally a word
fregante Nov 27, 2022
74ae360
Drop mention of Strict Mode
fregante Nov 28, 2022
f6037ef
Merge branch 'main' into old-no-typeof-undefined
fregante Dec 3, 2022
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2 changes: 2 additions & 0 deletions docs/rules/no-typeof-undefined.md
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Expand Up @@ -9,6 +9,8 @@

Checking if a value is `undefined` by using `typeof value === 'undefined'` is needlessly verbose. It's generally better to compare against `undefined` directly. The only time `typeof` is needed is when a global variable potentially does not exists, in which case, using `globalThis.value === undefined` may be better.

Historical note: Comparing against `undefined` without `typeof` was frowned upon until ES5. This is no longer a problem since all engines currently in use no longer allow reassigning the `undefined` global.
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@fregante fregante Nov 28, 2022 •
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Is this more correct? It seems that IE9 did this correctly already according to http://kangax.github.io/compat-table/es5/ (IE8 tests missing)

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Indeed broken on IE8 👍

Screen Shot 10

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Brokener on IE9 😂

Screen Shot 11


## Fail

```js
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