# stop using var❗️

[JS](/web/js.md) ⟩ [variable](/web/js/variable.md) ⟩ [var](/web/js/variable/declare/var.md) ⟩ stop using var:exclamation:

{% hint style="warning" %}

* [var is a statement❗️](/web/js/variable/declare/var/var-is-a-statement.md)(<mark style="color:orange;">**side effects**</mark>)
* [global var / function is global object property❗️](/web/js/variable/declare/var/is-global-obj-prop.md)(<mark style="color:orange;">**side effect**</mark>)
* [accessing var before declaration gets undefined❗️](/web/js/variable/declare/var/accessing-var-before-declaration-gets-undefined.md)(<mark style="color:red;">**unexpected result**</mark>)
* [var has no block scope❗️](/web/js/variable/declare/var/in-block-cant-shadow.md) (<mark style="color:red;">**unexpected result**</mark>)
* [var in block can't shadow outer let❗️](/web/js/variable/declare/var/var-in-block-cant-shadow-outer-let.md)(<mark style="color:red;">**unexpected result**</mark>)
* [var can shadow parameter even in strict mode❗️](/web/js/variable/declare/var/param-by-var.md)(<mark style="color:yellow;">**bad practice**</mark>)
* [var redeclaration applied even in strict mode❗️](/web/js/variable/declare/var/redeclare.md)(<mark style="color:yellow;">**bad practice**</mark>)
  {% endhint %}

{% tabs %}
{% tab title="👥 相關" %}

* [statement expected❗️](/web/js/grammar/statement/statement-expected.md):exclamation:
* :white\_check\_mark: [always use strict mode](/web/js/concept/env/js-engine/mode/strict-mode/always.md)
  {% endtab %}

{% tab title="📘 手冊" %}

* [ ] [Statements and declarations](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements) ⟩ [declaring variables](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements#declaring_variables) ⟩ [var](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/var)
* [ ] [Difference between statements and declarations](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements#difference_between_statements_and_declarations) ⭐️⭐️⭐️ ❗️❗️❗️
  {% endtab %}
  {% endtabs %}


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