# identifier 'xxx' has already been declared❗️

[JS](../..) ⟩ [error](..) ⟩ [SyntaxError]() ⟩ identifier 'xxx' has already been declared

{% hint style="danger" %}
⛔ <mark style="color:red;">**SyntaxError**</mark>: <mark style="color:yellow;">**identifier**</mark> 'xxx' <mark style="color:yellow;">**has already been declared**</mark>
{% endhint %}

{% tabs %}
{% tab title="✨ 範例" %}
* [in-block-cant-shadow](../../variable/declare/var/in-block-cant-shadow "mention"):no\_entry:
* [var-in-block-cant-shadow-outer-let](../../variable/declare/var/var-in-block-cant-shadow-outer-let "mention"):no\_entry:
* [no-redeclare](../../variable/declare/let/no-redeclare "mention"):no\_entry:
{% endtab %}

{% tab title="📗 參考" %}
* [ ] [ydkjs-scope-and-closures-v.2](../../../master/ref/book/you-dont-know-js-series-v.2/ydkjs-scope-and-closures-v.2 "mention") ⟩ [Ch. 1: What's the Scope?](https://github.com/getify/You-Dont-Know-JS/blob/2nd-ed/scope-closures/ch1.md#chapter-1-whats-the-scope)
{% endtab %}
{% endtabs %}
