CODEWITHSUNDEEP
c#javascriptasp.net-mvcstring
user1162850
user1162850

Reputation: 101

Javascript / ASP.NET MVC 4 - Using C# Strings in Javascript

I need to be able to access strings held in my C# code in JavaScript. To test, I have tried displaying a message box with the C# string in JavaScript (I am using this string literal and the message box as an example scenario):

alert(<%: "TEST" %>);

When this code runs, no message box is displayed. On the other hand, a message box is displayed with this code:

alert(<%: 6 %>);

Why is it that I can use integers but not strings? Is there any way around this?

Thanks.

Upvotes: 1

Views: 952

Answers (3)

p.s.w.g
p.s.w.g

Reputation: 149010

The problem is in how this translates into JavaScript:

alert(<%: "TEST" %>);

becomes 

alert(TEST);

This is a problem because it assumes there is a variable named TEST that you'd like to display the value of, but most likely, TEST is undefined. What you probably want to do is this:

alert('<%: "TEST" %>');

But since this is MVC 4, you can use the Json.Encode method to be a little cleaner, like this:

alert(<%: Json.Encode("TEST") %>);

Both of thse will translate to

alert('TEST');

This should display a message box with the string 'TEST'.

Upvotes: 0

Michael Liu
Michael Liu

Reputation: 55359

You need to add quotes around the string; otherwise, the browser sees alert(TEST);, which is incorrect. To prevent cross-site scripting attacks, you also need to properly escape special characters. Calling HttpUtility.JavaScriptStringEncode lets you do both:

alert(<%= HttpUtility.JavaScriptStringEncode("TEST", true) %>);

Note: If this JavaScript snippet appears inside an HTML attribute like onclick, you may need to change <%= to <%: so that the double quotes are also HTML encoded.

Upvotes: 5

T.J. Crowder
T.J. Crowder

Reputation: 1074168

Why is it that I can use integers but not strings?

Because you need to put strings in quotes:

alert("<%: "TEST" %>");

The key here, as always, is to look at what the browser actually receives. With your original code, what the browser sees is:

alert(TEST);

...which is trying to use the variable TEST, not a literal string.

Now in the above, I've assumed the string won't have any " in it or other things that aren't valid within a JavaScript string literal. That's not usually a good assumption to make.

If you're using a recent version of .Net or using JSON.Net (see this question for details), you can output the string using a JSON serializer, which will ensure that anything within it that may be problematic is properly encoded/escaped. For instance, with JSON.Net, you might use:

// With JSON.Net
alert(<%: JsonConvert.ToString("TEST") %>);

// With a recent version of .Net
alert(<%: HttpUtility.JavaScriptStringEncode("TEST", true) %>);

Upvotes: 0

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