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Added "NaN is not NaN" #375

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Added "NaN is not NaN" #375

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added "NaN is not NaN"
shreyas-a Oct 9, 2017
5eec4cd
corrections
shreyas-a Oct 10, 2017
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13 changes: 13 additions & 0 deletions doc/en/types/equality.md
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Expand Up @@ -18,6 +18,7 @@ JavaScript features *weak typing*. This means that the equality operator
false == null // false
null == undefined // true
" \t\r\n" == 0 // true
NaN == NaN // false

The above table shows the results of the type coercion, and it is the main reason
why the use of `==` is widely regarded as bad practice. It introduces
Expand All @@ -43,6 +44,7 @@ operator does **not** perform type coercion between its operands.
false === null // false
null === undefined // false
" \t\r\n" === 0 // false
NaN === NaN // false

The above results are a lot clearer and allow for early breakage of code. This
hardens code to a certain degree and also gives performance improvements in case
Expand All @@ -63,6 +65,17 @@ Here, both operators compare for **identity** and **not** equality; that is, the
will compare for the same **instance** of the object, much like `is` in Python
and pointer comparison in C.

### Comparing NaN
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@peterjwest peterjwest Oct 9, 2017 •
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I'm not quite sure about this explanation, according to my testing and research any equality with NaN, double or triple, returns false.

I would suggest an alternate explanation:

Any equality comparison with `NaN` will return `false`. This includes comparing `NaN` with itself, making it the only value in JavaScript which doesn't equal itself.

I don't think it's relevant here to talk about the type of NaN, although that should probably be added in the typeof section.

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I've referred to this ecma standards explanation

If either side of double equals `a == b` contains `NaN`, `false` will be returned.
In case of a tripple equals `a === b`, following things are considered.
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Typo triple

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fixed


FYI `typeof NaN` is `number`

- If `typeof a` is different from `typeof b`, return `false`.
- If `typeof a` is `number`, then
- If a is NaN, return `false`.
- If b is NaN, return `false`.

### In Conclusion

It is highly recommended to only use the **strict equality** operator. In cases
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