C# - Passing C# Variable to JavaScript

Question

I have the following line of code in C#:

Page.ClientScript.RegisterStartupScript(Page.GetType(), null, "window.open('http://localhost:4000/Transaction_Number.aspx?num=<%=trans_number%>', '_newtab')", true);

Now, trans_number is a variable in my C# code-behind. My problem is that when I process the query string (num variable), the result is always:

<%trans_number%>

instead of the contents of that variable. How can I solve this?

Answer 1

I think, you can resolve this pretty easily... Maybe:

Page.ClientScript.RegisterStartupScript(Page.GetType(), null, "window.open('http://localhost:4000/Transaction_Number.aspx?num=" + trans_number + "', '_newtab')", true);

Answer 2

You have a string that concatenates with a variable and is in turn embedded within another string. Issues like this tend to go away when you use intermediate variables and String.Format method:

string url = String.Format(@"http://localhost:4000/Transaction_Number.aspx?num={0}", trans_number);
string js = String.Format("window.open('{0}', '_newtab')", url);
Page.ClientScript.RegisterStartupScript(Page.GetType(), null, js, true);