JavaScript in HTML: unexpected outputs

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  • Tony Gahlinger
    #1

    JavaScript in HTML: unexpected outputs

    [My initial posting didn't seem to make it, so here's retry]

    I'm learning/experimenting with some simple JS/html markup, running
    an apache daemon and mozilla firefox browser in RH 9.

    Let's say I run the following markup with one or more of lines 6-10
    commented out:

    1 <html>
    2 <head>
    3 <script type="text/javascript">
    4 function showinfo()
    5 {
    6 width = window.screen.a vailWidth;
    7 document.write( "<br>screen width=\n");
    8 document.write( width);
    9 document.write( "<br>Date: ");
    10 document.write( Date());
    11 }
    12 </script>
    13 </head>
    14 <body onload="showinf o()">
    15 <p>

    My question: is there a simple explanation to account for the 'unexpected'
    behaviours below (Runs 1, 3, 5)?

    Run 1: nothing in 6-10 commented out; output (expected more):

    screen width=

    Run 2: line 7 commented out; output (as expected):

    1024
    Date: Wed Apr 14 2004 20:55:58 GMT-0400 (EDT)

    Run 3: lines 7, 9, 10 commented out; output (as expected, but unfinished loading):

    1024
    [ongoing hourglass indicating loading in progress]

    Run 4: lines 7, 10 commented out; output (as expected):

    1024

    Run 5: lines 7-9 commented out; output (as expected, but unfished loading):

    Date: Wed Apr 14 2004 22:46:49 GMT-0400 (EDT)

    I'm sure I'm missing something obvious. Helpful comments would be much appreciated.

    --Tony
    Tags: None
    • Richard Cornford
      #2
      Re: JavaScript in HTML: unexpected outputs

      Tony Gahlinger wrote:
      <snip>[color=blue]
      > 4 function showinfo()
      > 5 {
      > 6 width = window.screen.a vailWidth;
      > 7 document.write( "<br>screen width=\n");
      > 8 document.write( width);
      > 9 document.write( "<br>Date: ");
      > 10 document.write( Date());
      > 11 }
      > 12 </script>
      > 13 </head>
      > 14 <body onload="showinf o()">[/color]
      <snip>

      After a document has closed (which will have happened before the onload
      event) any call to - document.write - will clear and replace the current
      document with whatever is written. But the function - showinfo - is
      associated with the current document and is cleared, while it is
      executing. Unsurprisingly the consequences of removing the environment
      of a script while it is executing tend to be inconsistent and
      undesirable.

      If you want to call document.write after the current page has closed I
      would recommend outputting all of the new contents with just one call
      to - document.write - rather than several.

      Also, if a - document.open - call is made, or a - document.write - call
      is made on a document that is closed (which internally calls the open
      method when the document is not currently open), the document is not
      re-closed until the - document.close - method is called. Hence the
      impression that the page has not finished loading.

      Richard.


        Comment

        • Tony Gahlinger
          #3
          Re: JavaScript in HTML: unexpected outputs

          Richard Cornford wrote:[color=blue]
          > Tony Gahlinger wrote:
          > <snip>
          >[color=green]
          >> 4 function showinfo()
          >> 5 {
          >> 6 width = window.screen.a vailWidth;
          >> 7 document.write( "<br>screen width=\n");
          >> 8 document.write( width);
          >> 9 document.write( "<br>Date: ");
          >>10 document.write( Date());
          >>11 }
          >>12 </script>
          >>13 </head>
          >>14 <body onload="showinf o()">[/color]
          >
          > <snip>
          >
          > After a document has closed (which will have happened before the onload
          > event) any call to - document.write - will clear and replace the current
          > document with whatever is written. But the function - showinfo - is
          > associated with the current document and is cleared, while it is
          > executing. Unsurprisingly the consequences of removing the environment
          > of a script while it is executing tend to be inconsistent and
          > undesirable.
          >
          > If you want to call document.write after the current page has closed I
          > would recommend outputting all of the new contents with just one call
          > to - document.write - rather than several.
          >
          > Also, if a - document.open - call is made, or a - document.write - call
          > is made on a document that is closed (which internally calls the open
          > method when the document is not currently open), the document is not
          > re-closed until the - document.close - method is called. Hence the
          > impression that the page has not finished loading.
          >
          > Richard.[/color]

          Ah ... that makes sense all right; especially the reason for the unfinished
          loading (which one sees so often). Thanks!

          --Tony

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