Call by Value

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  • Mario Thiel
    #1

    Call by Value

    Hello,

    i am new to JavaScript and right now i am learning Call by Value. i
    tryed to write a small script but somehow it doesnt work right. i cant
    put <br> into it, and i can only put the document.write( xyz,x) in the
    function.

    <html>
    <head>
    <script language="JavaS cript">
    function Wert(x) {
    x += 5;
    document.write( xyz)
    document.write( x)//Why can i add an <br>?
    }
    </script>
    </head>
    <body>
    <script language="JavaS cript">
    var xyz = 10;
    Wert(xyz);
    Wert(x);
    //Why cant i put the document.write in here?
    </script>
    </body>
    </html>

    Greets from Germany

    Tags: None
    • Brian
      #2
      Re: Call by Value


      "Mario Thiel" <sepppel@freene t.de> wrote in message
      news:br4lf0$293 k27$1@ID-217726.news.uni-berlin.de...[color=blue]
      > Hello,
      >
      > i am new to JavaScript and right now i am learning Call by Value. i
      > tryed to write a small script but somehow it doesnt work right. i cant
      > put <br> into it, and i can only put the document.write( xyz,x) in the
      > function.
      >
      > <html>
      > <head>
      > <script language="JavaS cript">
      > function Wert(x) {
      > x += 5;
      > document.write( xyz)
      > document.write( x)//Why can i add an <br>?
      > }
      > </script>
      > </head>
      > <body>
      > <script language="JavaS cript">
      > var xyz = 10;
      > Wert(xyz);
      > Wert(x);
      > //Why cant i put the document.write in here?
      > </script>
      > </body>
      > </html>
      >
      > Greets from Germany
      >[/color]

      You are having a huge problem with variable scope. For instance, when you
      call Wert(x), X has never been declared. Also, this code never tries to
      write a <BR>. Basically, when you call Wert(x), you fail. Whatever is
      happening, you are likely failing with something, which is likely due to
      variable scope, and you are not finishing.

      Both xyz and x need to be in global scope. I have no idea what this code is
      supposed to due, but the following modifications will make everything work:

      <html>
      <head>
      <script language="JavaS cript">

      // Declare the variables as global, before they are used.
      var xyz = 10;
      var x = 0;

      function Wert(x) {
      x += 5;
      document.write( xyz)
      document.write( x)//Why can i add an <br>?
      document.write( "<BR>");
      }

      </script>
      </head>
      <body>
      <script language="JavaS cript">
      Wert(xyz);
      Wert(x);
      //Why cant i put the document.write in here?
      // Wert(x) will not fail any more, allowing you to proceed
      document.write( "WRITE IS WORKING, now");
      </script>
      </body>
      </html>


        Comment

        • @SM
          #3
          Re: Call by Value

          Mario Thiel a ecrit :
          [color=blue]
          > Hello,
          >
          > i am new to JavaScript and right now i am learning Call by Value. i
          > tryed to write a small script but somehow it doesnt work right. i cant
          > put <br> into it, and i can only put the document.write( xyz,x) in the
          > function.[/color]

          try that to understand a little
          [color=blue]
          > <html>
          > <head>
          > <script language="JavaS cript">
          > function Wert(x) {[/color]

          x=x*1; // to be sure x is a number
          [color=blue]
          > x += 5;[/color]

          /*
          [color=blue]
          > document.write( xyz)[/color]

          that is not correct ==> xyz is unknown
          you could do : */
          xy = 'hello world'
          document.write( x+'<hr><h2>'+xy +'</h2');
          [color=blue]
          > document.write( 'test with : '+x)//Why can i add an <br>?[/color]

          // because you have to tell it in JS ==> write('<br>');

          document.write( '<hr><h3>Addin g 5 times 1 to number : '+x+'</h3>');
          for(var i=1;i<6;i++)
          document.write( (x*1+i*1)+'<br> ');

          document.write( '<hr><h3>Geomet rical suite by 20 of number : '+x+'</h3>');
          for(var i=0;i<150;i+=20 )
          if(i>0)
          document.write( (x*i)+' = '+x+' * '+i+'<br>');

          document.write( '<p align=center>--- End of this test -----<p>');
          [color=blue]
          > }
          > </script>
          > </head>
          > <body>
          > <script language="JavaS cript">
          > var xyz = 10;
          > Wert(xyz);[/color]

          /*
          [color=blue]
          > Wert(x);[/color]

          */
          // you have to give a value to 'x'
          Werf(4); // Play with number 4
          document.write( '<h1>Other Number</h1>');
          Werf('15'); // Play with number 15
          [color=blue]
          > //Why cant i put the document.write in here?
          > </script>[/color]
          [color=blue]
          > </body>
          > </html>[/color]

          --
          *************** *************** *************** *************** **
          Stéphane MORIAUX : mailto:stephane OTER-MOImoriaux@wana doo.fr
          Aide aux Pages Perso (images & couleurs, formulaire, CHP, JS)
          http://perso.wanadoo.fr/stephanemoriaux/internet/

          *************** *************** *************** *************** **


            Comment

            • Mario Thiel
              #4
              Re: Call by Value

              Thanks you too, i see the mistake now. This script was just for
              understanding, not for having any purpose.

                Comment

                • Thomas 'PointedEars' Lahn
                  #5
                  Re: Call by Value

                  Mario Thiel wrote:
                  [color=blue]
                  > i am new to JavaScript and right now i am learning Call by Value.[/color]

                  JavaScript does not support call-by-value. It supports a special
                  kind of call-by-reference which differs from that you may be used
                  to:

                  function foobar(o, o2, p, i)
                  {
                  // Does not redefine the referenced object
                  // but uses `o' as local variable and assign
                  // it a primitive boolean value:
                  // "call-by-value"
                  o = false;
                  alert("foobar:: o = " + o) // false

                  // Changes the value of a property of the referenced object
                  // using the value of `i'
                  // "call-by-reference" for one, "call-by-value" for the other
                  o2.haha = i;

                  // Adds a property to the referenced object:
                  // "call-by-reference"
                  o2.bla = "blurb";

                  // Does not change the value of the global variable but uses
                  // `p' as local variable:
                  // "call-by-value"
                  p = Math.PI;
                  }

                  var x = 42;
                  var obj1 = {};
                  var obj2 = {};
                  obj2.haha = "333";

                  foobar(obj1, obj2, x, 999);

                  // "42 [object Object] 999 blurb undefined" (Mozilla/5.0)
                  alert(
                  x
                  + " " + obj1
                  + " " + obj2.haha
                  + " " + obj2.bla
                  + " " + typeof o);


                  PointedEars

                    Comment

                    • Lasse Reichstein Nielsen
                      #6
                      Re: Call by Value

                      Thomas 'PointedEars' Lahn <PointedEars@we b.de> writes:
                      [color=blue]
                      > Mario Thiel wrote:
                      >[color=green]
                      >> i am new to JavaScript and right now i am learning Call by Value.[/color]
                      >
                      > JavaScript does not support call-by-value. It supports a special
                      > kind of call-by-reference which differs from that you may be used
                      > to:[/color]

                      I guess that's a matter of philosophy. Javascript definitly passes
                      simple values (strings, numbers, booleans, null and undefined) by
                      value. The "problem" is objects, which are passed ... as objects.

                      I would still call it "call-by-value", it's just that the value of an
                      object is the object itself, not a copy of it (because objects have an
                      identity, an copy of an object would be a different object). It is
                      probably *implemente* by passing a reference, but it's not like you
                      can change what the reference points to (as with call-by-reference).

                      To me, Javascript is call-by-value (and so is, e.g., Java, but not
                      C# or C++)

                      /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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