# double tilde (\~\~)

[JS](https://lochiwei.gitbook.io/web/js) ⟩ [statement](https://lochiwei.gitbook.io/web/js/grammar/statement) ⟩ [expression](https://lochiwei.gitbook.io/web/js/grammar/statement/expr) ⟩ [operator](https://lochiwei.gitbook.io/web/js/grammar/op) ⟩ double tilde (\~\~)

{% hint style="success" %} <mark style="color:orange;">**nearest**</mark>**&#x20;**<mark style="color:yellow;">**integer**</mark>**&#x20;**<mark style="color:orange;">**towards**</mark> <mark style="color:red;">**0**</mark><mark style="color:yellow;">**.**</mark>

```javascript
// ⭐️ ~~(x) : nearest integer towards 0
~~(-5.5)        // -5
~~( 5.5)        //  5

+undefined      // ⭐️ NaN
~~undefined     // ⭐️ 0

// similar operators
!!x        // any -> bool
+x         // any -> number
```

:bulb: it's not really an operator, it's just <mark style="color:yellow;">`~~x === ~(~x)`</mark>.

:point\_right: [](https://lochiwei.gitbook.io/web/js/grammar/op/arithmetic/bitwise/not "mention") <mark style="color:yellow;">**|**</mark> :star2: [2s-complement](https://lochiwei.gitbook.io/web/js/grammar/op/arithmetic/bitwise/2s-complement "mention")
{% endhint %}

{% tabs %}
{% tab title="👥 相關" %}

* :scales: [vs.-math.trunc](https://lochiwei.gitbook.io/web/js/grammar/op/arithmetic/bitwise/not/vs.-math.trunc "mention")
* :heavy\_plus\_sign: [..](https://lochiwei.gitbook.io/web/js/grammar/op/arithmetic/bitwise "mention") ⟩ [](https://lochiwei.gitbook.io/web/js/grammar/op/arithmetic/bitwise/not "mention") - invert bits.
* :heavy\_plus\_sign: [unary](https://lochiwei.gitbook.io/web/js/grammar/op/arithmetic/unary "mention") ⟩ unary plus (+)&#x20;
* :heavy\_plus\_sign: [unary](https://lochiwei.gitbook.io/web/js/grammar/op/logical/unary "mention") ⟩ logical not (!)
  {% endtab %}

{% tab title="💈範例" %}
{% embed url="<https://codesandbox.io/embed/compare-math-trunc-bi2gh?fontsize=14&hidenavigation=1&theme=dark>" %}
"\~\~" vs. Math.trunc()
{% endembed %}

{% hint style="warning" %}
注意：使用 [JSON.stringify()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify) 將函數轉換成字串時，會轉成 "**undefined**"❗️
{% endhint %}
{% endtab %}

{% tab title="📗 參考" %}

* [ ] CodeWars ⟩ [Adding Big Numbers](https://www.codewars.com/kata/525f4206b73515bffb000b21)
  {% endtab %}

{% tab title="📘 手冊" %}

* [Bitwise NOT (\~)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_NOT)
* [Math.trunc()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/trunc) - same as <mark style="color:purple;">**`~~`**</mark> (with wider range)
  {% endtab %}

{% tab title="🗣 討論" %}

* SOF ⟩ [What does \~\~ ("double tilde") do in Javascript?](https://stackoverflow.com/a/4055675)
  {% endtab %}
  {% endtabs %}


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