How to pass a parameter name in JavaScript?

Question

Is there a way to get a handler to a variable dynamically in JavaScript? I think this won't make sense so here's what I'm trying to do.

I'm using JQuery Flot to generate graphs in my web app. Everything works fine until I have two graphs in the same page.

I get the data from the database using c# and convert it into a JavaScript array and write onto the page like this.

HTML/C#:

@{
        KII.Models.JsonPerformGraphData items = new KII.Models.JsonPerformGraphData();

        foreach (KII.Models.PerformanceGraphItem item in Model.PerformanceGraphItems)
        {
            items.Add(item);
        }

        <script type="text/javascript">

      @Html.Raw("var pgdata"+Model.Id+" = ")  @Html.Raw(items.toJson()) ;

        </script>
    }

Then, I call a method on document ready to draw the graph

JavaScript:

if ($(".PerformanceGraph")) {
        $(".PerformanceGraph").livequery(function () {
            //Display the graph for risk and reward.
            var options = { series: {
                bars: { show: true, barWidth: 0.45, align: "center" }
            },
                legend: {
                    show: true, position: "ne", backgroundOpacity: 0, container: $("#PerformanceGraphLegend")
                },
                multiplebars: true
            };


            var dataArray = $(this).attr('data-array');//I get the name of the variable as String.
            $.plot($(".PerformanceGraph"), pgdata, options);
        });
    }

pgdata from javascript must match "var pgdata"+Model.Id+" from HTML/C#.

How can I get the variable that the HTML/C# code spits out to the HTML?

Couldn't you just output something like this instead? plotMyJson({json from c#...}); and then create a plotMyJson function in js? — Dogbert
– Dogbert, Commented Jun 29, 2011 at 18:26

Kevin Coulombe · Accepted Answer · 2011-06-29 18:25:35Z

1

You could concatenate the variable name together and "eval" it.

http://www.w3schools.com/jsref/jsref_eval.asp

answered Jun 29, 2011 at 18:25

Kevin Coulombe

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2 Comments

Carlos Blanco Over a year ago

changing it to $.plot($(this), eval(dataArray), options); worked. I see eval is thought to be evil though.

digitalbath Over a year ago

eval is very evil, and is (almost) never the right way to accomplish whatever you're trying to accomplish.

digitalbath · Accepted Answer · 2011-06-29 18:32:33Z

1

Why not something like this?

<script type="text/javascript">
var pgdata = {};
@Html.Raw("pgdata["+Model.Id+"] = ")  @Html.Raw(items.toJson()) ;
</script>

and then in javascript you simply iterate over the keys in pgdata:

for (k in pgdata) {
    $.plot($(".PerformanceGraph"), pgdata[k], options);
}

answered Jun 29, 2011 at 18:32

digitalbath

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2 Comments

Carlos Blanco Over a year ago

The HTML/C# code gets executed several times. I think var pgdata = {}; will clear the array after each execution.

digitalbath Over a year ago

still, this general approach is what you're looking for. Instantiate and assign pgdata somewhere earlier, or do something like if (! ('pgdata' in window)) { pgdata = {}; }

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