Don't blow up when evaluate_script is called with a cyclic structure.

README.md

@@ -194,6 +194,9 @@ makes debugging easier). Running `rake autocompile` will watch the
     enables `:hover` effects etc to trigger before the click happens,
     which can affect the click in some cases. [Issue #120]
 
+*   Don't blow up when `evaluate_script` is called with a cyclic
+    structure.
+
 ### 0.7.0 ###
 
 #### Features ####

lib/capybara/poltergeist/client/agent.coffee

@@ -14,11 +14,17 @@ class PoltergeistAgent
       { error: { message: error.toString(), stack: error.stack } }
 
   @stringify: (object) ->
-    JSON.stringify object, (key, value) ->
-      if Array.isArray(this[key])
-        return this[key]
+    try
+      JSON.stringify object, (key, value) ->
+        if Array.isArray(this[key])
+          return this[key]
+        else
+          return value
+    catch error
+      if error instanceof TypeError
+        '"(cyclic structure)"'
       else
-        return value
+        throw error
 
   pushWindow: (new_window) ->
     @windows.push(new_window)

lib/capybara/poltergeist/client/compiled/agent.js

@@ -25,13 +25,21 @@ PoltergeistAgent = (function() {
   };
 
   PoltergeistAgent.stringify = function(object) {
-    return JSON.stringify(object, function(key, value) {
-      if (Array.isArray(this[key])) {
-        return this[key];
+    try {
+      return JSON.stringify(object, function(key, value) {
+        if (Array.isArray(this[key])) {
+          return this[key];
+        } else {
+          return value;
+        }
+      });
+    } catch (error) {
+      if (error instanceof TypeError) {
+        return '"(cyclic structure)"';
       } else {
-        return value;
+        throw error;
       }
-    });
+    }
   };
 
   PoltergeistAgent.prototype.pushWindow = function(new_window) {

spec/integration/session_spec.rb

@@ -293,5 +293,16 @@ describe Capybara::Session do
         @session.status_code.should == 402
       end
     end
+
+    it 'ignores cyclic structure errors in evaluate_script' do
+      code = <<-CODE
+        (function() {
+          var a = {}
+          a.a = a
+          return a
+        })()
+      CODE
+      @session.evaluate_script(code).should == "(cyclic structure)"
+    end
   end
 end