Ping.js initial upload.

ping.js

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+/**
+ * Creates and loads an image element by url.
+ * @param  {String} url
+ * @return {Promise} promise that resolves to an image element or
+ *                   fails to an Error.
+ */
+var request_image = function(url) {
+    return new Promise(function(resolve, reject) {
+        var img = new Image();
+        img.onload = function() { resolve(img); };
+        img.onerror = function() { reject(url); };
+        img.src = url + '?random-no-cache=' + Math.floor((1 + Math.random()) * 0x10000).toString(16);
+    });
+};
+
+/**
+ * Pings a url.
+ * @param  {String} url
+ * @return {Promise} promise that resolves to a ping (ms, float).
+ */
+var ping = function(url) {
+    return new Promise(function(resolve, reject) {
+        var start = (new Date()).getTime();
+        var response = function() { 
+            var delta = ((new Date()).getTime() - start);
+
+            // HACK: Use a fudge factor to correct the ping for HTTP bulk.
+            delta /= 4;
+
+            resolve(delta); 
+        };
+        request_image(url).then(response).catch(response);
+
+        // Set a timeout for max-pings, 5s.
+        setTimeout(function() { reject(Error('Timeout')); }, 5000);
+    });
+};