feat: add utility helper for returning promises or using callbacks

Author: mbroadst

lib/utils.js

@@ -693,6 +693,42 @@ function* makeCounter(seed) {
   }
 }
 
+/**
+ * Helper function for either accepting a callback, or returning a promise
+ *
+ * @param {Function} [callback] an optional callback.
+ * @param {Function} fn A function that takes a callback
+ * @returns {Promise|void} Returns nothing if a callback is supplied, else returns a Promise.
+ */
+function maybePromise(callback, fn) {
+  let result;
+  if (typeof callback !== 'function') {
+    result = new Promise((resolve, reject) => {
+      callback = (err, res) => {
+        if (err) return reject(err);
+        resolve(res);
+      };
+    });
+  }
+
+  fn(function(err, res) {
+    if (err != null) {
+      try {
+        callback(err);
+      } catch (error) {
+        return process.nextTick(() => {
+          throw error;
+        });
+      }
+      return;
+    }
+
+    callback(err, res);
+  });
+
+  return result;
+}
+
 module.exports = {
   filterOptions,
   mergeOptions,
@@ -722,5 +758,6 @@ module.exports = {
   MongoDBNamespace,
   resolveReadPreference,
   emitDeprecationWarning,
-  makeCounter
+  makeCounter,
+  maybePromise
 };