add evalulate_on_new_document — fixes #132

alexanderadam · alexanderadam · commit ae629389cc37 · 2021-02-25T20:42:36.000+01:00
#132
diff --git a/README.md b/README.md
@@ -124,7 +124,6 @@ browser.mouse
 browser.quit
 ```
 
-
 ## Docker
 
 In docker as root you must pass the no-sandbox browser option:
@@ -775,6 +774,18 @@ browser.add_script_tag(content: "window.__injected = 42")
 browser.evaluate("window.__injected") # => 42
 ```
 
+#### evaluate_on_new_document(javascript)
+
+Evaluate JavaScript to modify things before a page load:
+
+```ruby
+javascript = <<~JS
+    Object.defineProperty(navigator, 'languages', {
+      get: function() { return ['tlh']; }
+    });
+  JS
+browser.evaluate_on_new_document javascript
+```
 
 ## Frames
 
diff --git a/lib/ferrum/browser.rb b/lib/ferrum/browser.rb
@@ -77,6 +77,10 @@ def extensions
       end
     end
 
+    def evaluate_on_new_document(javascript)
+      extensions << javascript
+    end
+
     def timeout
       @timeout || DEFAULT_TIMEOUT
     end
diff --git a/spec/browser_spec.rb b/spec/browser_spec.rb
@@ -205,6 +205,25 @@ module Ferrum
           browser&.quit
         end
       end
+
+      it 'supports user Javascript' do
+        begin
+          javascript = <<~JS
+            Object.defineProperty(navigator, 'languages', {
+              get: function() { return ['tlh']; }
+            });
+          JS
+
+          browser = Browser.new.tap { |b| b.evaluate_on_new_document(javascript) }
+          browser.go_to(base_url('/ferrum/with_user_js'))
+
+          browser_language = browser.evaluate('document.getElementById("browser-languages").innerHTML')
+
+          expect(browser_language).to eq('tlh')
+        ensure
+          browser&.quit
+        end
+      end
     end
 
     context "javascript errors" do
diff --git a/spec/support/views/with_user_js.erb b/spec/support/views/with_user_js.erb
@@ -0,0 +1,15 @@
+<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
+  <head>
+    <meta http-equiv="Content-type" content="text/html; charset=utf-8"/>
+    <title>ferrum with_user_js</title>
+  </head>
+  <body>
+     <dl>
+      <dt>languages</dt>
+      <dd id="browser-languages"></dd>
+    </dl>
+    <script>
+      document.getElementById('browser-languages').innerHTML = navigator.languages;
+    </script>
+  </body>
+</html>
