En versiones previas de NodeJS / JavaScript en el Navegador, habrías usado "callbacks". Lo que lleva al "callback hell".

## Coroutines { #coroutines }

    e: IOException,
  )

  /**
   * Called when the HTTP response was successfully returned by the remote server. The callback may
   * proceed to read the response body with [Response.body]. The response is still live until its
   * response body is [closed][ResponseBody]. The recipient of the callback may consume the response
   * body on another thread.
   *

*   Added `tf.keras.layers.SpectralNormalization` layer wrapper to perform spectral normalization on the weights of a target layer.

                Request
                  .Builder()
                  .url(server.url("/a"))
                  .build()
              try {
                val callbackA = RecordingCallback()
                client.newCall(requestA).enqueue(callbackA)
                callbackA.await(requestA.url).assertBody("a")
              } catch (e: Exception) {
                throw RuntimeException(e)
              }
            }

- Added `kubectl node drain` helper callbacks `OnPodDeletionOrEvictionStarted`
  and `OnPodDeletionOrEvictionFailed`; people extending `kubectl` can use these
  new callbacks for more granularity. Deprecated the `OnPodDeletedOrEvicted`
  node drain helper callback. ([#117502](https://github.com/kubernetes/kubernetes/pull/117502), [@adilGhaffarDev](https://github.com/adilGhaffarDev))

            // Result should be either Unicode or ASCII fallback depending on default charset
            String expectedUnicode = String.valueOf(icon.getUnicodeChar());
            String expectedAscii = icon.getAsciiFallback();
            assertTrue(
                    result.equals(expectedUnicode) || result.equals(expectedAscii),
                    "Result should be either Unicode or ASCII fallback for " + icon + ", got: " + result);
        }
    }

 */
package okhttp3.internal

import java.net.InetAddress
import okhttp3.Dns

/**
 * A network that always resolves two IP addresses per host. Use this when testing route selection
 * fallbacks to guarantee that a fallback address is available.
 */
class DoubleInetAddressDns : Dns {
  override fun lookup(hostname: String): List<InetAddress> {
    val addresses = Dns.SYSTEM.lookup(hostname)

     * handleAllCompleted(), they will already have been nulled out. But in the case of
     * whenAll*().call*(), this future may be pending until the callback runs -- or even longer in
     * the case of callAsync(), which waits for the callback's returned future to complete.
     */
    releaseResources(ALL_INPUT_FUTURES_PROCESSED);
  }

  /**

  companion object {
    /**
     * A network that resolves only one IP address per host. Use this when testing route selection
     * fallbacks to prevent the host machine's various IP addresses from interfering.
     */
    private val SINGLE_INET_ADDRESS_DNS =
      Dns { hostname ->
        val addresses = Dns.SYSTEM.lookup(hostname)

        loadIncludes(path, sp, callback);
        substitute(sp, callback);
        sp.forEach(properties::setProperty);
    }

    public static void substitute(MavenProperties props, UnaryOperator<String> callback) {
        for (Enumeration<?> e = props.propertyNames(); e.hasMoreElements(); ) {
            String name = (String) e.nextElement();