Add fail callback and missing docstrings to params (#357)

Co-authored-by: Matt Vollrath <matt@endpoint.com>
Co-authored-by: Matthijs van der Burgh <MatthijsBurgh@outlook.com>
Co-authored-by: Jihoon Lee <jihoonlee.in@gmail.com>
Co-authored-by: Ezra Brooks <ezra@brooks.cx>

src/core/Param.js

@@ -25,8 +25,10 @@ function Param(options) {
  *
  * @param {function} callback - Function with the following params:
  * @param {Object} callback.value - The value of the param from ROS.
+ * @param {function} [failedCallback] - Function when the service call failed with the following params:
+ * @param {string} failedCallback.error - The error message reported by ROS.
  */
-Param.prototype.get = function(callback) {
+Param.prototype.get = function(callback, failedCallback) {
   var paramClient = new Service({
     ros : this.ros,
     name : '/rosapi/get_param',
@@ -40,16 +42,18 @@ Param.prototype.get = function(callback) {
   paramClient.callService(request, function(result) {
     var value = JSON.parse(result.value);
     callback(value);
-  });
+  }, failedCallback);
 };
 
 /**
  * Set the value of the param in ROS.
  *
  * @param {Object} value - The value to set param to.
- * @param {function} callback - The callback function.
+ * @param {function} [callback] - The callback function.
+ * @param {function} [failedCallback] - The callback function when the service call failed.
+ * @param {string} failedCallback.error - The error message reported by ROS.
  */
-Param.prototype.set = function(value, callback) {
+Param.prototype.set = function(value, callback, failedCallback) {
   var paramClient = new Service({
     ros : this.ros,
     name : '/rosapi/set_param',
@@ -61,15 +65,17 @@ Param.prototype.set = function(value, callback) {
     value : JSON.stringify(value)
   });
 
-  paramClient.callService(request, callback);
+  paramClient.callService(request, callback, failedCallback);
 };
 
 /**
  * Delete this parameter on the ROS server.
  *
- * @param {function} callback - The callback function.
+ * @param {function} [callback] - The callback function when the service call succeeded.
+ * @param {function} [failedCallback] - The callback function when the service call failed.
+ * @param {string} failedCallback.error - The error message reported by ROS.
  */
-Param.prototype.delete = function(callback) {
+Param.prototype.delete = function(callback, failedCallback) {
   var paramClient = new Service({
     ros : this.ros,
     name : '/rosapi/delete_param',
@@ -80,7 +86,7 @@ Param.prototype.delete = function(callback) {
     name : this.name
   });
 
-  paramClient.callService(request, callback);
+  paramClient.callService(request, callback, failedCallback);
 };
 
 module.exports = Param;