### What it does
Checks for binding to underscore prefixed variable without side-effects.

### Why is this bad?
Unlike dead code, these bindings are actually
executed. However, as they have no effect and shouldn't be used further on, all they
do is make the code less readable.

### Known problems
Further usage of this variable is not checked, which can lead to false positives if it is
used later in the code.

### Example
```
let _i_serve_no_purpose = 1;
```