Help for a newbie JavaScript student

[Hannahb]

I've just started learning JavaScript and I'm already stumped. I have this code:

var mytest1 = new String();
mytest1.setNumber( 2 );

var mytest2 = new String();
mytest2.setNumber( 3 );

if( mytest1 + mytest2 == 5 ) alert('Success!');

But nothing is happening when I run it! What am I missing or doing wrong? Help would be much appreciated. I'm sure it's something stupid.

Thanks all,
Hannah

[Arno_Adams]

Hi,

setNumber is no standard method for strings in javascript.

HTH, Tom

[Hannahb]

Thanks for your reply. What should I use instead?

[adb64]

Hannahb, welcome to WebmasterWorld!

mytest1 and mytest2 are declared as strings, adding like you did will not result in a value of 5 but in a string with value "23".

if( mytest1 + mytest2 == "23" ) alert('Success!');

That will probably work (I didn't check however)

[Hannahb]

Or is the use of "String" the problem?

[Hannahb]

Hi adb64. Thanks for your answer. I tried changing to "23", but that didn't work either. Just a blank screen. :(

[adb64]

Hi Hannahb,
I've tried and check javascript string object and like Arno_Adams (AKA Tom) mentions, setNumber is not a method for the string object.
What exactly do you want to achieve?

[Hannahb]

It's for an assignment for my class. Maybe it would be best to post the original question.

Write the missing implementation of Test to make this code work and the
alert appear:

var mytest1 = new Test();
mytest1.setNumber( 2 )

var mytest2 = new Test();
mytest2.setNumber( 3 );

if( mytest1 + mytest2 == 5 ) alert('Success!')

[Little_G]

Hi,

You need to override the Object class's valueOf method.
Like this:

function Test(){
   this.number;
   this.setNumber = function(number){
      this.number = number;
   }
   this.valueOf = function(){
      return this.number;
   }
}

The valueOf method tells the JavaScript interpreter how to convert the object into a primitive, in this case a Test object into an int.

Core JavaScript 1.5 Reference:Global Objects:Object:valueOf - MDC [developer.mozilla.org]

Andrew

[edited by: Little_G at 11:26 am (utc) on July 17, 2008]

[Hannahb]

It worked! Thank you so much! :)