[HtmlUnit] [ htmlunit-Bugs-1576162 ] Cannot read property "prototype" - Scriptaculous 1.6.4

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Bugs item #1576162, was opened at 2006-10-12 19:48
Message generated for change (Comment added) made by vguna
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Category: None
Group: 1.8
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Matt Raible (mraible)
Assigned to: Nobody/Anonymous (nobody)
Summary: Cannot read property "prototype" - Scriptaculous 1.6.4

Initial Comment:
I tried upgrading my app to use the latest version of
Script.aculo.us,
but it spits out the following error:

C:\Source\temp\appfuse\test\web\web-tests.xml:28: Canoo
Webtest: R_1393.
Test failed.
Test step invoke
(C:\Source\temp\appfuse\test\web\login.xml:1: )
named "get Login Page" failed with
 message "Step[invoke "get Login Page" (1/6)]: Script
error loading
page executing webtest at: invok
e TypeError: Cannot read property "prototype" from null
(http://localhost:9234/appfuse/scripts/prototype.js#1320)

Line 1320 is:

copy(Form.Methods, HTMLFormElement.prototype);

The full method is:

Element.addMethods = function(methods) {
  Object.extend(Element.Methods, methods || {});

  function copy(methods, destination) {
    var cache = Element.extend.cache;
    for (var property in methods) {
      var value = methods[property];
      destination[property] = cache.findOrStore(value);
    }
  }

  if (typeof HTMLElement != 'undefined') {
    copy(Element.Methods, HTMLElement.prototype);
    copy(Form.Methods, HTMLFormElement.prototype);
    [HTMLInputElement, HTMLTextAreaElement,
HTMLSelectElement].each(function(klass) {
      copy(Form.Element.Methods, klass.prototype);
    });
    _nativeExtensions = true;
  }
}

Also posted to Canoo WebTest mailing list, but got no
response: 

http://www.nabble.com/Issues-with-build1393-and-1416-with-Script.aculo.us-1.6.4-tf2412243.html

The version of HtmlUnit that WebTest uses is 1.9.

----------------------------------------------------------------------

Comment By: veit (vguna)
Date: 2007-02-17 11:16

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Hi.

Any news on this? I've got the same problem with Script.aculo.us 1.7 and
Canno Webtest snapshot (=html unit 1.10).

regards,
Veit


----------------------------------------------------------------------

Comment By: Marc Guillemot (mguillem)
Date: 2006-11-13 10:22

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gpolya, you're workaround is interesting. Best would be to
fix the problem in htmlunit itself.
Daniel Gredler already sent me a patch to make htmlunit DOM
Level 2 HTML API conform js class names. I (or he) will
apply it soon. Nevertheless it seems it is just a part of
the solution.

Btw, as you seem to already have a good understanding of
htmlunit, if you provide some patches showing that you're
able to contribute to htmlunit's development, I would be
glad to propose you as committer.

----------------------------------------------------------------------

Comment By: Pólya (gpolya)
Date: 2006-11-13 09:50

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After taking a close look at the HtmlUnit source code, I
found a better solution. Instead of commenting  the
offending lines out we can provide the missing javascript
classes by using the following ScriptPreProcessor:

<code>
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;

import com.gargoylesoftware.htmlunit.ScriptPreProcessor;
import com.gargoylesoftware.htmlunit.html.HtmlElement;
import com.gargoylesoftware.htmlunit.html.HtmlPage;
import com.gargoylesoftware.htmlunit.javascript.host.Form;
import com.gargoylesoftware.htmlunit.javascript.host.Input;
import com.gargoylesoftware.htmlunit.javascript.host.Select;
import com.gargoylesoftware.htmlunit.javascript.host.Textarea;


/**
 * <a href="http://prototype.conio.net">Prototype 1.5.0</a>
uses classes of the
 * DOM Level 2 HTML API, which htmlunit 1.10 does not
support. This java script 
 * pre-processor adds the classes that are needed, when
prototype.js is loaded.
 * The implementations of the classes do not cover 100% of
the API, but are close
 * enough for testing.
 */
public class PrototypeJSPreProcessor implements
ScriptPreProcessor {
  
  public static class HTMLFormElement extends Form {
    public String getClassName() {
      return "HTMLFormElement";
    }
  }

  public static class HTMLInputElement extends Input {
    public String getClassName() {
      return "HTMLInputElement";
    }
  }
  
  public static class HTMLTextAreaElement extends Textarea {
    public String getClassName() {
      return "HTMLTextAreaElement";
    }
  }
  
  public static class HTMLSelectElement extends Select {
    public String getClassName() {
      return "HTMLSelectElement";
    }
  }
  
  /**
   * Defines the classes <code>HTMLFormElement</code>,
<code>HTMLInputElement</code>, 
   * <code>HTMLTextAreaElement</code>, and
<code>HTMLSelectElement</code>
   * when prototype.js is loaded.
   * 
   * @see
com.gargoylesoftware.htmlunit.ScriptPreProcessor#preProcess(com.gargoylesoftware.htmlunit.html.HtmlPage,
java.lang.String, java.lang.String,
com.gargoylesoftware.htmlunit.html.HtmlElement)
   */
  public String preProcess(HtmlPage page, String scriptCode,
String scriptName, HtmlElement element) {
    if(scriptName.endsWith("prototype.js")) {
      try {
        Scriptable window =
(Scriptable)page.getEnclosingWindow().getScriptObject();
        ScriptableObject.defineClass(window,
HTMLFormElement.class);
        ScriptableObject.defineClass(window,
HTMLInputElement.class);
        ScriptableObject.defineClass(window,
HTMLTextAreaElement.class);
        ScriptableObject.defineClass(window,
HTMLSelectElement.class);
      } catch(Exception e) {
        throw new RuntimeException(e);
      }
    }
    return scriptCode;
  }

}
</code>

The reason Prototype 1.5.0 (or Scriptaculous 1.6.4) is not
working is the following: Prototype uses classes of the DOM
Level 2 HTML API which HtmlUnit so far doesn't provide.
Prototype actually checks for the API by checking if the
class HTMLElement exists. If HTMLElement exists, it assumes
the API is present. This is in my opinion a bug in
Prototype. Coincidentally HTMLElement exists in HTMLUnit,
but not as part of the DOM Level 2 HTML API. This, however,
is in my opinion a bug in HtmlUnit.

----------------------------------------------------------------------

Comment By: Marc Guillemot (mguillem)
Date: 2006-11-13 09:45

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We will try to integrate Prototype's unit test to be run
with htmlunit to ensure that htmlunit is "Prototype
compatible" (idea from Daniel Gredler).

----------------------------------------------------------------------

Comment By: Pólya (gpolya)
Date: 2006-11-10 17:15

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You can just comment the offending lines out. You don't need
to actually change the prototype.js itself; you can use a
script pre-processor to do that:

<code>
    WebClient webClient = new WebClient();

    // This is needed as htmlunit 1.10 cannot handle
prototype 1.5.0_rc1
    webClient.setScriptPreProcessor(new ScriptPreProcessor() {
      public String preProcess(HtmlPage page, String
scriptCode, String scriptName, HtmlElement element) {
        if(scriptName.endsWith("prototype.js")) {
          // comment the couple of lines out htmlunit can't
handle
          scriptCode =
scriptCode.replaceFirst("copy\\(Element\\.Methods,
HTMLElement\\.prototype\\);", "/*copy(Element.Methods,
HTMLElement.prototype);");
          scriptCode =
scriptCode.replaceFirst("_nativeExtensions = true;",
"_nativeExtensions = true;*/");
        }
        return scriptCode;
      }
    });
</code>

I'm not a prototype expert, so I can't really say if that
has some nasty side effects. But I didn't have any problems
after making this change. I used HtmlUnit 1.10 and Prototype
1.5.0_rc1 directly without WebTest or Scriptaculous.

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