Throttler.swift

// MARK: - Throttler
public class Throttler {
    private let queue: DispatchQueue = DispatchQueue.global(qos: .background)
    private var job: DispatchWorkItem = DispatchWorkItem(block: {})
    private var previousRun: Date = Date.distantPast
    private var maxInterval: Double
    
    init(seconds: Double) {
        self.maxInterval = seconds
    }
    
    func throttle(block: @escaping () -> Void) {
        job.cancel()
        job = DispatchWorkItem() { [weak self] in
            self?.previousRun = Date()
            block()
        }
        let delay = maxInterval.isLess(than: Date.second(from: previousRun)) ? 0 : maxInterval
        queue.asyncAfter(deadline: .now() + Double(delay), execute: job)
    }
}

// MARK: - Date extension
private extension Date {
    static func second(from referenceDate: Date) -> Double {
        return Date().timeIntervalSince(referenceDate)
    }
}

using source code from here: http://danielemargutti.com/2017/10/19/throttle-in-swift/