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appengine/swarming/elements/res/imp/common/common-behavior.html

Index: appengine/swarming/elements/res/imp/common/common-behavior.html
diff --git a/appengine/swarming/elements/res/imp/common/common-behavior.html b/appengine/swarming/elements/res/imp/common/common-behavior.html
index 4aefc6b700acf9b6d5ac08ecd982003c36a968e6..25c61710200c3d5ec02eda7da52568b6532e597b 100644
--- a/appengine/swarming/elements/res/imp/common/common-behavior.html
+++ b/appengine/swarming/elements/res/imp/common/common-behavior.html
@@ -11,8 +11,9 @@
       behaviors: [SwarmingBehaviors.CommonBehavior]
   in the creation of any Polymer element.
 
-  SwarmingBehaviors.CommonBehavior contains shared functions to ease
-  templating, such as _or() and _not().
+  SwarmingBehaviors.CommonBehavior contains shared methods to ease
+  templating, such as _or() and _not() as well as general utility methods
+  such as _getJsonAsync.
  -->
 
 <script>
@@ -21,6 +22,38 @@
     // This behavior wraps up all the shared swarming functionality.
     SwarmingBehaviors.CommonBehavior = {
 
+      // _getJsonAsync makes an XHR to a url, parses the response as JSON
+      // and sticks the resulting object into the property with the name given
+      // by "bindTo". If busy is defined, the property with that name will be
+      // set to true while the request is in flight and false afterwards.
+      // request headers (e.g. authentication) and query params will be used if
+      // provided. Query params is an object like {String:Array<String>}. On
+      // error, bindTo will be set to false.  It is not set to undefined
+      // because computed values in Polymer don't fire if a property is
+      // undefined. Clients should check that bindTo is not falsey.
+       _getJsonAsync: function(bindTo, url, busy, headers, params) {
+        if (!bindTo || !url) {
+          console.log("Need at least a polymer element to bind to and a url");
+          return;
+        }
+        if (busy) {
+          this.set(busy, true);
+        }
+        url = url + "?" + sk.query.fromParamSet(params);
+        sk.request("GET", url, "", headers).then(JSON.parse).then(function(json){
+          this.set(bindTo, json);
+          if (busy) {
+            this.set(busy, false);
+          }
+        }.bind(this)).catch(function(reason){
+          console.log("Reason for failure of request to " + url, reason);
+          this.set(bindTo, false);
+          if (busy) {
+            this.set(busy, false);
+          }
+        }.bind(this));
+      },
+
       _not: function(a) {
         return !a;
       },