This can be used to export any error log automatically to a text file. Feel free to use for your project!

ExportErrorToFile.js

// SWIFT 4.0.1
// XCODE 9.0.1

#if DEBUG
    var errorFile = "errorLog.txt"
    // Error object must be conform to CustomStringConvertible protocol
    func saveErrorLog<T: CustomStringConvertible>(error: T) {
        // Fetch document directory URL
        let documentDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
        let path = documentDirectory.appendingPathComponent(errorFile).path
        
        print("Document Directory path : \(path)")
        
        var stringFromFile = ""
        // If "errorFile" is exist then read
        do {
            stringFromFile = try String.init(contentsOfFile: path, encoding: .utf8)
        }catch let error as NSError {
            print(error.localizedDescription)
        }
        
        // Write
        do {
            try "\(stringFromFile)\(Date())\n\(error.description)\n\n".write(toFile: path, atomically: true, encoding: .utf8)
        }catch let error as NSError {
            print(error.localizedDescription)
        }
    }
    #endif