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Re: [caplet] Re: Javascript mystery

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  • Mike Samuel
    The below causes the same symptoms in both squarefree shells: var f = document.createElement( iframe ); document.body.appendChild(f); with (f.contentWindow) {
    Message 1 of 13 , Oct 10, 2007
      The below causes the same symptoms in both squarefree shells:
            var f = document.createElement('iframe');
            with (f.contentWindow) {
              (function foo() { alert(this + ' : ' + (this === window)); }).call(null);

      If the goal is to detect at the beginning of a function body whether `this` is the global scope, I don't think there's any underlying equivalence between between 'this' and 'window' in a normal browser environment, but it does raise questions for applications that execute javascript cross-frame.


      On 10/10/2007, Mike Samuel <mikesamuel@...> wrote:

      On 10/10/2007, Mike Samuel < mikesamuel@...> wrote:
      The reason for this is in the first line of the bookmarklet
          with(window.open(...)) { ... }

      Each window object has an eponymous property, 'window'.

      This 'with' block causes apparent globals to instead be interpreted as properties of the opened window, so this may still be the window that was in focus when you clicked the bookmark, but this.window !== this, since this.window is resolved as a property of the window.

      I tried deleting the window and assigning window to this, but rerunning it doesn't change behavior.  I think that may be a

      err assigning window to this -> assigning window to this.window

      cross-domain thing though.  window's are manipulable across domain since a window needs to be able to set a frame's location, but they don't allow setting of arbitrary properties such as "window" cross-domain.


      On 10/10/2007, Mike Samuel <mikesamuel@...> wrote:
      To make sure I'm clear, you're using the square free bookmarklet (the first entry, [shell], at http://www.squarefree.com/bookmarklets/webdevel.html ) not http://www.squarefree.com/shell/shell.html.

      And then you do
        function foo() { print(this); print(this === window); }
      and you get the output

      I can repeat using the squarefree bookmarklet, but not the shell webpage.

      On 10/10/2007, Mark S. Miller <erights@...> wrote:

      On 10/9/07, Mike Samuel <mikesamuel@...> wrote:
      > I can't repeat your example under the squarefree shell on FF2.0.0.7 on Linux.
      > And I can't reproduce by playing around with 'with' blocks, window subclasses, or eval.call.

      I've just repeated it on FF2.0.0.7 on Linux. For all the tests I've
      done on both, I haven't yet seen any difference between FF on Linux
      vs. Mac. Ben's msg led to some more experiments:

      When I try this using the standalone squarefree shell page at
      http://www.squarefree.com/shell/shell.html I don't get the peculiar
      behavior. It only happens when I use the squarefree shell bookmarklet
      available from http://www.squarefree.com/bookmarklets/webdevel.html .
      When using the bookmarklet, it does open the shell up in a different
      window from the one it's examining. The mystery window from my example
      is the bookmarklet's new window. Typing

      function foo() {return this;}

      into the bookmarklet's shell does cause it to close itself.


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