Assign a unique filename to each file.

uniqueFileName.js

...        
        var fileName = file.name;
        // Assign a unique name (uFileName) to each file (fileName
        // + randnum)to ensure client will not attempt to use same
        //set of keys for multiple files of the same name.
        var uFileName = `${fileName}|${Math.random()}`;
        // Set temporary storage location in /tmp/
        var dest = fs.createWriteStream(`/tmp/${uFileName}`);
...