this vs self vs document

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  • Wow
    #1

    this vs self vs document

    when calling a object in an html, should I use self.objectname
    this.objectname or document.object name?

    for example, i have a form called theform and a link called thelink

    i can call
    document.thefor m, but not document.thelin k

    i can use both this.theform and this.thelink and self.theform and
    self.thelink.

    WHY? why thelink can not be called from document?


    Tags: None
    • Wow
      #2
      Re: this vs self vs document

      It is clearly stated that link is an object under document. Read this gif
      file
      Understanding Router Login & IP Addresses | Your Networking Essentials
      http://www.comptechdoc.org/independent/web/cgi/javamanual/objheirarchy.gif
      Dive into our comprehensive guide to understanding router login processes, IP addresses like 192.168.1.1, 10.0.0.1, and more. Learn how to access and manage your router's settings, check your private IP, and optimize your network using our easy step-by-step guide.

      [color=blue]
      > when calling a object in an html, should I use self.objectname
      > this.objectname or document.object name?
      >
      > for example, i have a form called theform and a link called thelink
      >
      > i can call
      > document.thefor m, but not document.thelin k
      >
      > i can use both this.theform and this.thelink and self.theform and
      > self.thelink.
      >
      > WHY? why thelink can not be called from document?
      >
      >[/color]


        Comment

        • Grant Wagner
          #3
          Re: this vs self vs document

          Wow wrote:
          [color=blue]
          > It is clearly stated that link is an object under document. Read this gif
          > file
          > http://www.comptechdoc.org/independe...jheirarchy.gif
          >[color=green]
          > > when calling a object in an html, should I use self.objectname
          > > this.objectname or document.object name?
          > >
          > > for example, i have a form called theform and a link called thelink
          > >
          > > i can call
          > > document.thefor m, but not document.thelin k
          > >
          > > i can use both this.theform and this.thelink and self.theform and
          > > self.thelink.
          > >
          > > WHY? why thelink can not be called from document?[/color][/color]

          In most user agents, the name of the form is made a property of the document
          object, the names of anchor tags are not (although in IE, the names and ids of
          pretty much everything are made members of the global (window in most Web
          browsers) object. This leads to the sort of confusion you are having.

          The best way to reference objects is by their fully qualified path in the DOM
          hierarchy:

          document.forms['formName'].elements['elementName']

          To access links on the page, you have a variety of options, the most
          cross-browser compatible method is to use the links collection of the document
          object:

          document.links[indexOfLinkOnPa ge] or document.links[nameOrIdOfLink] (note that
          using the name/id may not work in all browsers)

          As for a discussion of self, this and document. Your question seems to
          indicate a fundamental lack of understanding. In simple terms:

          "document" refers to the default HTMLDocument object created by the user agent
          when a page is rendered, typically document is a property of the global
          (window) object

          "self" is also a property of the global (window) object, one which points back
          at the window object such that (window.self === window) should be true (it
          isn't in Internet Explorer, but it is in Gecko-based browsers, Netscape 4.78
          and Opera 7.53). I'm unsure why people use "self". It requires JavaScript to
          step through the object in the DOM you actually want to retrieve a property
          which points back at the object you wanted in the first place. I guess it's
          useful for self-documenting code (pun not intended). I don't know, I never use
          it, when I want the default window object, I use "window".

          "this" always refers to the current object. Outside of any function, "this"
          would refer to the global (window) object such that (this === window) returns
          true. Within functions, "this" can refer to a number of things, but it is
          always the "current object". Example:

          <body onload="documen t.links[0].onclick = onclickHandler; ">
          <script type="text/javascript">
          function onclickHandler( ) {
          alert(
          "'this' is 'window': " +
          (this === window) +
          "\n" +
          "'this' is 'document.links[0]': " +
          (this === document.links[0])
          );
          return false;
          }
          </script>
          <a href="#">'this' will refer to 'document.links[0]'</a><br />
          <a href="#" onclick="return onclickHandler( );">'this' will refer to
          'window'</a>
          </body>

          Same event handler code, same event (onclick) attached on the same type of
          element, but "this" refers to a different thing for each link. If you wanted a
          reference to the link that triggered the event for the second link, you'd
          need:

          <a href="#" onclick="return clickHandler(th is);">

          As for that image, it's old, outdated and actually just wrong. "window" is not
          a property of "navigator" . If it were, (navigator.wind ow === window) would be
          true. It's not. In fact, navigator.windo w is undefined in every user agent I
          tested. You _might_ be able to say that diagram is a representation of the DOM
          hierarchy (which is different from a JavaScript object heirarchy) in Netscape
          4, but I wouldn't even go that far. You'd be best served by simply removing
          any bookmarks you have to that page.

          --
          Grant Wagner <gwagner@agrico reunited.com>
          comp.lang.javas cript FAQ - http://jibbering.com/faq


            Comment

            • Lasse Reichstein Nielsen
              #4
              Re: this vs self vs document

              "Wow" <a@alexa.com> writes:
              [color=blue]
              > when calling a object in an html,[/color]

              You mean "When referring to ...". In Javascript, the word "call"
              should be reserved for what you do to functions :)
              [color=blue]
              > should I use self.objectname
              > this.objectname or document.object name?[/color]

              No. They are all wrong for some browser.

              The "this" operator can refer to many different objects, depending on
              where you use it. Often it will be either the global object (the same
              referred to by the global variables "self" and "window") or the
              document. In either case, it is better to know which one is used and
              do it explicitly.

              IE is known for making named HTML elements available as global
              variables of the same name (i.e., as "self.objectnam e",
              "window.objectn ame" or plain "objectname "). It will fail in Mozilla,
              so it's a bad choice.

              Netscape, and later Mozilla, makes some named HTML elements available
              as identically named properties of the document object. Some other
              browsers also make some elements available this way (typically forms),
              but there are also exceptions. It's very often also a bad choice.

              That leaves none of the above, so what is a coder to do?
              [color=blue]
              > for example, i have a form called theform and a link called thelink
              >
              > i can call
              > document.thefor m, but not document.thelin k[/color]

              As I said, forms are typically avaiable directly as properties of the
              document. Links are not.
              [color=blue]
              > i can use both this.theform and this.thelink and self.theform and
              > self.thelink.[/color]

              You are using IE.
              [color=blue]
              > WHY? why thelink can not be called from document?[/color]

              Because it isn't there. None of these ways to access the elements are
              part of any standard. However, There are wasy, almost universally
              implemented and standard compliant ways to access both forms and links.

              document.forms['theform']
              and
              document.links['thelink']
              You'll never need to use anything else (and shouldn't either).

              Good luck.
              /L
              --
              Lasse Reichstein Nielsen - lrn@hotpop.com
              DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
              'Faith without judgement merely degrades the spirit divine.'

                Comment

                • Lasse Reichstein Nielsen
                  #5
                  Re: this vs self vs document

                  "Wow" <a@alexa.com> writes:
                  [color=blue]
                  > It is clearly stated that link is an object under document. Read this gif
                  > file
                  > http://www.comptechdoc.org/independe...jheirarchy.gif[/color]

                  Don't rely on that image for any exact information. It is, at best, a
                  rough sketch of relations between some types of objects in a browser.

                  There is no "Language" Object, the image just says that Array, etc., are
                  parts of the language. There is a "navigator" object, but it's a child
                  of the window object, not the other way around. Perhaps "Navigator" merely
                  refers to the browser itself. The children of "Document" are the types
                  of elements that are available in collections (like forms and links),
                  except that it seems this was written for an early Netscape browser (the
                  only ones to have an active document.layers collection).

                  So, forget that image. I think it confuzes you more than it helps.

                  /L
                  --
                  Lasse Reichstein Nielsen - lrn@hotpop.com
                  DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
                  'Faith without judgement merely degrades the spirit divine.'

                    Comment

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