Relate unhandled rejections to source calls

index.js

@@ -4,11 +4,26 @@ exports.fromCallback = function (fn) {
   return Object.defineProperty(function (...args) {
     if (typeof args[args.length - 1] === 'function') fn.apply(this, args)
     else {
+      // Capture stack trace of where the promise was created in case it rejects.
+      let caller_stack = new Error("Failing function was called from here").stack
       return new Promise((resolve, reject) => {
         fn.call(
           this,
           ...args,
-          (err, res) => (err != null) ? reject(err) : resolve(res)
+          (err, res) => {
+            if (err != null) {
+              if (err instanceof Error && typeof err.stack === 'string') {
+                // It is safe to improve the error's stack trace with
+                // information about where the Promise was created and where
+                // the err was passed from.
+                let e = new Error("Callback-based function called back with an error")
+                err.stack += "\n" + e.stack + "\n" + caller_stack
+              }
+              reject(err)
+            } else {
+              resolve(res)
+            }
+          }
         )
       })
     }