Javascript and struts

[Jay Abrahm]

Hi,

The problem I have touches both scripting and struts. Since I though it was most closely related to scripting I have put it in this forum but please move the thread if this is not the right forum.

	function resetColors() {
		var a = '<s:property value="colorList"/>';
		alert('a = '+a);
                // Code to reset the right select list to the preselected colors
	}	

The alerted output is

a = {1=blue, 5=Green}

How can I substring a to get the key 1 and 5. I have tried a[0] and other options. I guess I need someone to point me to the right API.

[Eric Pascarello]

can you change the data in colorList?

If you can change it to look like this:

{"1":"blue", "5":"Green"}

and change your code to look like this:

var a = <s:property value="colorList"/>;  

You can do this

alert(a["1"]);

Eric

[Jay Abrahm]

I think I understood where you are heading. Are you thinking about pushing it into a JSON.

The problem there is that the data in the colorList is a linkedHashMap. Unfortunately design prevents me from changing the Map.

[Eric Pascarello]

And you can not write a method that converts it into another format?

Eric

[Jay Abrahm]

The display in the form a = {1=blue, 5=Green} is done by javascript when it processes the Map.

My use case needs it to be a Map since it is used across screens but I guess I can process it at the server side and have an additional request variable with the same data in JSON format.

Basically my question would be - if javascript is able to process the HashMap and alert it properly. Wouldn't there be an API to access it.

[Eric Pascarello]

You would have to write a function that takes the string and splits it up.

var a = '{1=blue, 5=Green}';
var b = a.replace(/[\{\}]/g,"").split(/,\s?/g);
var len = b.length;

var c = {};
for(var i=0;i<b.length;i++){
  var temp = b[i].split("=");
  c[temp[0]] = temp[1];
}

alert(c["1"]);

It would be a lot more efficient if you do it on the server if the hash map is large.

Eric

[Jay Abrahm]

Hi Eric,

Thanks for replying, yep that did work. Also, I got it to work from the server side...

Sorry for being persistent but I just cannot find an explanation from anywhere on how javascript was able to convert the collection into a var. Again, sorry for repeating myself - If javascript can do that so wouldnt it have some way to access the complex object that it has created.

Anyways, Eric, thanks for the help...

[Eric Pascarello]

JavaScript does not know what a hashmap is. It is like me trying to read a book in German. I know there is a bunch of text there, I have no clue what it says until I get it translated.

Eric

[Jay Abrahm]

Eric Pascarello wrote:JavaScript does not know what a hashmap is

How was it able to 'translate' it and get a = {1=blue, 5=Green}. It should have just failed but javascript realized that the collection contents needs to be processed and it did process to give a set instead of undefined or object or something else.

Maybe I am pushing it without understanding the core of what javascript does...

[Eric Pascarello]

Problem is that {1=blue, 5=Green} is not a valid object syntax, hence it has no clue what to do with it. When I read the German book, I am undefined too.

If you were to run this
var a = {1=blue, 5=Green}

it should give you the error SyntaxError: missing : after property id

Proper JSON notation is
var a = {"1":"blue", "5":"Green"}
which JS knows how to process it.


If you return it as
var a = '{1=blue, 5=Green}';
It is a plain old string and plain old strings are just that.

So you had two choices, you either make it work from the server spitting out JSON, or you hire an interpreter on the client [that function I wrote] that converts a string over. You need to remember that you are trying to make Apple Juice from an Orange. It is impossible to make JavaScript do something that Java understands. I wish my wife would understand that it is impossible for me to do the dishes, but she insists I make Apple juice from Oranges!

Eric

[Sean Clark]

Personally I am a fan of doing things like this server side, especially since the JSON api is actually very good (granted it's not doing anything especially complicated) but still it is good.

Are there actually any advantages doing it one way over another?

[Cloudgen C.F. Wong]

Eric Pascarello wrote:You would have to write a function that takes the string and splits it up.

var a = '{1=blue, 5=Green}';
var b = a.replace(/[\{\}]/g,"").split(/,\s?/g);
var len = b.length;

var c = {};
for(var i=0;i<b.length;i++){
  var temp = b[i].split("=");
  c[temp[0]] = temp[1];
}

alert(c["1"]);

It would be a lot more efficient if you do it on the server if the hash map is large.

Eric

Dear Eric,

Your code can be simplified using an inline replace() method as:

<script type="text/javascript">
var a = '{1=blue, 5=Green}',c={};
a.replace(/\s*/g,"").replace(/(\w+)=(\w+)/g,function(s,s1,s2){c[s1]=s2});
alert(c["1"]);
</script>

[Eric Pascarello]

I did not feel like messing with reg exp when I wrote it.

Eric

[Cloudgen C.F. Wong]

Eric Pascarello wrote:I did not feel like messing with reg exp when I wrote it.

Eric

Yes, Regular Expression make code less "readability". I wonder which code will run faster, using split or using regex, any clue? Maybe I do the benchmark test later.

[Jay Abrahm]

Wow !! I didnt check my mails for two days and look what happened...

Thanks Eric for helping me understand.

Since the Map was pretty huge, I moved the translation to the server and transported it as a JSON. Taking a quick look at it I though it was quicker but I haven't actually generated any stats to check if there really was any performance improvement.

[Eric Pascarello]

JavaScript is normally slow with large loops so it is always better to do it on the server that is built to handle that.

Eric