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How to get Page.ResolveUrl to Work in JavaScript

KyleMit

Relative References With ~ in JavaScript

The problem is that as far as ASP.NET is concerned, the content delivered in your .js file is a string. It does not apply any sort of rendering before IIS delivers it. It gets the same treatment any other content file would, like a .jpg or .png.

In order to call server side methods (like ResolveUrl), you need to use the <% ... %> syntax within any page that is parsed by ASP.NET (like an .aspx or .master file).

By the way, these little code blocks go by a lot of different names:

Inline Expressions

Embedded Code Blocks

Code Nuggets

Server Side Script Delimiters

Code Render Blocks

ASP Directives

In particular, we want a Displaying Expression with the syntax <%= ... %>, where:

the value that is entered after the equals sign is written into the current page

Knowing that, we can build our own own URL by using ResolveClientUrl() which:

returns a URL string suitable for use by the client to access resources on the Web server

To this, we'll pass in the Web Application Root Operator or ~ character, where ASP.NET:

resolves the ~ operator to the root of the current application:

By combining these, we can save the result of the displaying expression into a JavaScript variable by placing the following code on your Master Page (adapted from Joel Varty's blog):

<script type="text/javascript">
    var baseUrl = '<%= Page.ResolveClientUrl("~/") %>';
</script>

Since JavaScript variables are inherently global, any other script can now access the baseUrl variable, so we can utilize it from the .js file with the following script:

function ResolveUrl(url) {
    return url.replace("~/", baseUrl);
}

Now you can call ResolveUrl("~/DynamicMenu.ashx") directly from your javascript file and it will create the appropriate URL by stripping out "~/" and replacing it with the baseUrl created earlier by the server side script.