What do `dfile` and `tfile` mean? Maybe use longer / more descriptive variable names. Also if `dfile` is only used as an alias to `prefix` (and isn't otherwise modified), just set

````
var tfile = this.uploadDir + prefix;
````

Creating a variable only to use it immediately, unless you're simplifying a calculation or concatenation, is a bit confusing, looks like there's more going on than there is.