30 lines
1.2 KiB
Markdown
30 lines
1.2 KiB
Markdown
---
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title: What is the only value not equal to itself in JavaScript?
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shortTitle: The only value not equal to itself
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type: question
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language: javascript
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tags: [type,comparison]
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author: chalarangelo
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cover: eagle
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excerpt: Did you know there's a JavaScript value that's not equal to itself?
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dateModified: 2021-12-12T05:00:00-04:00
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---
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`NaN` (Not-a-Number) is the only JavaScript value not equal to itself when comparing with any of the comparison operators. `NaN` is often the result of meaningless or invalid math computations, so it doesn't make sense for two `NaN` values to be considered equal.
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```js
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const x = Math.sqrt(-1); // NaN
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const y = 0 / 0; // NaN
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x === y; // false
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x === NaN; // false
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Number.isNaN(x); // true
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Number.isNaN(y); // true
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isNaN(x); // true
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isNan('hello'); // true
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```
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You can check for `NaN` values using the `Number.isNaN()` function. Note that this is different from the original , global `isNaN()`. Their difference lies in the fact that `isNaN()` forcefully converts its argument to a number, whereas `Number.isNaN()` doesn't. This is why `Number.isNaN()` is considered more robust and preferable in most cases.
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