---
title: Rule block-scoped-var
layout: doc
---
<!-- Note: No pull requests accepted for this file. See README.md in the root directory for details. -->

# Treat var as Block Scoped (block-scoped-var)

The `block-scoped-var` rule generates warnings when variables are used outside of the block in which they were defined. This emulates C-style block scope.

## Rule Details

This rule aims to reduce the usage of variables outside of their binding context and emulate traditional block scope from other languages. This is to help newcomers to the language avoid difficult bugs with variable hoisting.

Examples of **incorrect** code for this rule:

```js
/*eslint block-scoped-var: "error"*/

function doIf() {
    if (true) {
        var build = true;
    }

    console.log(build);
}

function doIfElse() {
    if (true) {
        var build = true;
    } else {
        var build = false;
    }
}

function doTryCatch() {
    try {
        var build = 1;
    } catch (e) {
        var f = build;
    }
}
```

Examples of **correct** code for this rule:

```js
/*eslint block-scoped-var: "error"*/

function doIf() {
    var build;

    if (true) {
        build = true;
    }

    console.log(build);
}

function doIfElse() {
    var build;

    if (true) {
        build = true;
    } else {
        build = false;
    }
}

function doTryCatch() {
    var build;
    var f;

    try {
        build = 1;
    } catch (e) {
        f = build;
    }
}
```

## Further Reading

* [JavaScript Scoping and Hoisting](http://www.adequatelygood.com/JavaScript-Scoping-and-Hoisting.html)
* [var Hoisting](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/var#var_hoisting)

## Version

This rule was introduced in ESLint 0.1.0.

## Resources

* [Rule source](https://github.com/eslint/eslint/tree/master/lib/rules/block-scoped-var.js)
* [Documentation source](https://github.com/eslint/eslint/tree/master/docs/rules/block-scoped-var.md)
