Curious to know what and why is correct?

I'm asking because I'm never sure what to use when.

This:

```
function foo(){
    $('.bar')
        .click(function(){
            var baq = 'baz';
        })
}

```

Or this

```
function foo(){
    var baq;
    $('.bar')
        .click(function(){
            baq = 'baz';
        })
}

```

And also this:

```
function foo(){
    $('.bar')
        .click(function(){
            let baq = 'baz';
        })
}

```

Or this

```
function foo(){
    let baq;
    $('.bar')
        .click(function(){
            baq = 'baz';
        })
}

```