Assign a raw HTML tag to a JavaScript variable

Question

I'm working on an existing ASP.Net application and came across an interesting piece of JavaScript that I've been wondering about.

A few variables are being declared as literals, and they aren't in strings. For example, something like this is done:

<script type="text/javascript">  
    var jsonData = <asp:Literal ID="MyJsonObject" runat="server" />;
    ......
</script>

And in the server side code(C#), these tags are actually being altered from a JsonTextWriter similarly to this:

var stringBuilder = new StringBuilder();
var stringWriter = new StringWriter(stringBuilder);

using (var jsonWriter = new JsonTextWriter(stringWriter))
{
    jsonWriter.Formatting = Formatting.Indented;

    jsonWriter.WriteStartObject();
    jsonWriter.WritePropertyName("someProperty");
    jsonWriter.WriteValue("someValue");
    jsonWriter.WriteEndObject();
}

MyJsonObject.Value = stringBuilder.ToString();

This in turn is causing the jsonData variable to be able to be used as a Json object in the client side code.

What I've noticed is, if I put single quotes around the tag and change it to:

<script type="text/javascript">  
    var jsonData = '<asp:Literal ID="MyJsonObject" runat="server" />';
    ......
</script>

This doesn't work as it's no longer coming across as a Json object, but as an actual string. However, as I would expect, when it's just a plain tag, I'm receiving several syntax errors from Visual Studio.

So my question is:

Is this something that's generally acceptable or should I avoid keeping things like this around? Yeah, it works, but it doesn't look right to me.

I've found a few different questions that seem to be related here, but none seem to provide any insight on my particular situation.

Shotgun Ninja · Accepted Answer · 2015-06-10 18:19:42Z

2

In short: Yes, this looks acceptable. That appears to be one of the intended use-cases of the <asp:Literal> tag. Since you're writing a Javascript object literal, you won't even need the single-quotes, since that will change how the code works.

The thing to note is that <asp:Literal> isn't an HTML tag, and therefore will not make it to the user as it is. The <asp:Literal> tag gets pre-processed by ASP.NET before the page is sent to the user (since you have runat="server" specified); therefore, it will be processed regardless of surrounding content and replaced entirely with the resolved string value. Thus, your rendered page will be transformed (on the server-side) from this:

var jsonData = <asp:Literal ID="MyJsonObject" runat="server" />;

to this:

var jsonData = {
    "someProperty" : "someValue"
};

This is a good way of transferring rich data constructed on the server-side into the client-side Javascript without having to write out raw Javascript to the page.

If you wanted a JSON-formatted string instead, then doing what you're doing and calling JSON.stringify(jsonData) afterwards would be your best bet.

answered Jun 10, 2015 at 18:19

Shotgun Ninja

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2 Comments

Jon Over a year ago

This is exactly the kind of response I was looking for. I suppose the syntax errors from Visual Studio had me curious, as I've never seen something like it before. I was able to eliminate the errors at one point by using hidden fields, but that took some extra effort and ended up being some excessive clutter. Thanks for the explanation!

Shotgun Ninja Over a year ago

Fun part is, the last time I touched ASP in general was over 6 years ago; I work with JSPs and JSP Tag Libraries, and they're similar enough to have this particular issue in common.

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