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# babel-plugin-undeclared-variables-check
> This plugin throws a compile-time error on references to undeclared variables.
## Example
**In**
```javascript
function foo() {}
foo();
bar();
```
**Out**
```
ReferenceError: stdin: Line 3: Reference to undeclared variable "bar" - did you mean "foo"?
1 | function foo() {}
2 | foo();
> 3 | bar();
| ^
4 |
```
## Installation
```sh
npm install --save-dev babel-plugin-undeclared-variables-check
```
## Usage
### Via `.babelrc` (Recommended)
**.babelrc**
```json
{
"plugins": ["undeclared-variables-check"]
}
```
### Via CLI
```sh
babel --plugins undeclared-variables-check script.js
```
### Via Node API
```javascript
require("babel-core").transform("code", {
plugins: ["undeclared-variables-check"]
});
```