Swift 4 Version

extension String {

init(htmlEncodedString: String) {
    self.init()
    guard let encodedData = htmlEncodedString.data(using: .utf8) else {
        self = htmlEncodedString
        return
    }

    let attributedOptions: [NSAttributedString.DocumentReadingOptionKey : Any] = [
        NSAttributedString.DocumentReadingOptionKey(rawValue: .documentType.rawValue): NSAttributedString.DocumentType.html,
        NSAttributedString.DocumentReadingOptionKey(rawValue: .characterEncoding.rawValue): String.Encoding.utf8.rawValue
    ]

    do {
        let attributedString = try NSAttributedString(data: encodedData, options: attributedOptions, documentAttributes: nil)
        self = attributedString.string
    } catch {
        print("Error: \(error)")
        self = htmlEncodedString
    }
  }
}