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Refactor common code from compose into a util function.

Trac #1455, #1448

(imported from commit 6fb691ac952b833655584b05f6caedaefe41c1a0)

zephyr/static/js/util.js

@@ -253,5 +253,15 @@ exports.array_compare = function util_array_compare(a, b) {
     return true;
 };
 
+exports.xhr_error_message = function (message, xhr) {
+    if (xhr.status.toString().charAt(0) === "4") {
+        // Only display the error response for 4XX, where we've crafted
+        // a nice response.
+        message += ": " + $.parseJSON(xhr.responseText).msg;
+    }
+    return message;
+};
+
+
 return exports;
 }());