Sample

StorageService.swift

import Foundation
import UIKit
import FirebaseStorage

struct StorageService {
    // provide method for uploading images
    static func uploadImage(_ image: UIImage, at reference: StorageReference, completion: @escaping (URL?) -> Void) {
        guard let imageData = UIImageJPEGRepresentation(image, 0.5) else {
            return completion(nil)
        }
        
        reference.putData(imageData, metadata: nil, completion: { (metadata, error) in
            
            if let error = error {
                assertionFailure(error.localizedDescription)
                return completion(nil)
            }
            
            completion(metadata?.downloadURL())
        })
    }
}