# try-catch-finally

* [JS](/web/js.md) ⟩ [statement](/web/js/grammar/statement.md) ⟩ [control flow](/web/js/grammar/statement/flow.md) ⟩ [jump](/web/js/grammar/statement/flow/jump.md) ⟩ try-catch-finally
* [JS](/web/js.md) ⟩ [error](/web/js/err.md) ⟩ [handling](/web/js/debug/handling.md) ⟩ try-catch-finally 

{% hint style="success" %}
([statement](/web/js/grammar/statement.md)) 

```javascript
try { ... }            // run code that may throw.
catch (err) { ... }    // error handling (and∨ rethrow)
finally { ... }        // cleanup code
```

{% endhint %}

{% tabs %}
{% tab title="🧨 雷區" %}
{% hint style="danger" %}
一但使用 <mark style="color:blue;">`try`</mark>，一定要用 <mark style="color:blue;">`catch(err)`</mark> 去抓「<mark style="color:yellow;">**所有的錯誤**</mark>」，否則可能會<mark style="color:red;">**漏掉**</mark>「<mark style="color:yellow;">自己沒有預期的錯誤</mark>」:exclamation:

```javascript
try {
  noSuchFunc();  // ⛔ ReferenceError (not catched)
} catch(err) { 
  // `console.log(err)` omitted ... (dangerous)❗
  // or, `throw err` omitted ...
}
// the code will continue executing happily❗
```

{% endhint %}
{% endtab %}

{% tab title="⭐️ 重點" %}
{% hint style="warning" %}
if a <mark style="color:purple;">**finally clause**</mark> <mark style="color:yellow;">**issues**</mark> a [return](/web/js/grammar/statement/flow/jump/return.md) <mark style="color:yellow;">**statement**</mark>, the method <mark style="color:yellow;">**returns**</mark>**&#x20;**<mark style="color:green;">**normally**</mark>, even if an exception has been thrown and has not yet been handled.
{% endhint %}

{% hint style="info" %} <mark style="color:yellow;">**bare**</mark>**&#x20;**<mark style="color:purple;">**catch clause**</mark>

in <mark style="color:yellow;">**ES2019**</mark> and later, the [**parentheses**](/web/js/grammar/token/punctuator/parentheses.md) / (<mark style="color:blue;">`error`</mark>) [**identifier**](/web/js/grammar/token/id.md) in the catch clause <mark style="color:green;">**can**</mark>**&#x20;**<mark style="color:yellow;">**be omitted**</mark>.
{% endhint %}
{% endtab %}

{% tab title="👥 相關" %}

* [error handling](/web/js/debug/handling.md)
* [throw](/web/js/debug/handling/throw.md)
  {% endtab %}

{% tab title="📗 參考" %}

* [ ] [JavaScript: The Definitive Guide](/web/master/ref/javascript-the-definitive-guide.md) ⟩ 5.5.7 try/catch/finally
  {% endtab %}

{% tab title="📘 手冊" %}

* [try...catch](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try...catch)
  {% endtab %}
  {% endtabs %}


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