1 files changed, 69 insertions, 0 deletions
diff --git a/docs/src/callback.js b/docs/src/callback.js
new file mode 100644
index 00000000..aaf69cde
--- /dev/null
+++ b/docs/src/callback.js
@@ -0,0 +1,69 @@
+function noop(){}
+
+function chain(delegateFn, explicitDone){
+  var onDoneFn = noop;
+  var onErrorFn = function(e){
+    console.error(e.stack || e);
+    process.exit(-1);
+  };
+  var waitForCount = 1;
+  delegateFn = delegateFn || noop;
+  var stackError = new Error('capture stack');
+
+  function decrementWaitFor() {
+    waitForCount--;
+    if (waitForCount == 0)
+      onDoneFn();
+  }
+
+  function self(){
+    try {
+      return delegateFn.apply(self, arguments);
+    } catch (error) {
+      self.error(error);
+    } finally {
+      if (!explicitDone)
+        decrementWaitFor();
+    }
+  };
+  self.onDone = function(callback){
+    onDoneFn = callback;
+    return self;
+  };
+  self.onError = function(callback){
+    onErrorFn = callback;
+    return self;
+  };
+  self.waitFor = function(callback){
+    if (waitForCount == 0)
+      throw new Error("Can not wait on already called callback.");
+    waitForCount++;
+    return chain(callback).onDone(decrementWaitFor).onError(self.error);
+  };
+
+  self.waitMany = function(callback){
+    if (waitForCount == 0)
+      throw new Error("Can not wait on already called callback.");
+    waitForCount++;
+    return chain(callback, true).onDone(decrementWaitFor).onError(self.error);
+  };
+
+  self.done = function(callback){
+    decrementWaitFor();
+  };
+
+  self.error = function(error) {
+    var stack = stackError.stack.split(/\n\r?/).splice(2);
+    var nakedStack = [];
+    stack.forEach(function(frame){
+      if (!frame.match(/callback\.js:\d+:\d+\)$/))
+        nakedStack.push(frame);
+    });
+    error.stack = error.stack + '\nCalled from:\n' + nakedStack.join('\n');
+    onErrorFn(error);
+  };
+
+  return self;
+}
+
+exports.chain = chain;