Ruby variable in JavaScript throws syntax error

Question

I have a Rails controller action that initializes this variable:

@print_url = new_batch_batch_content_template_path(@batch, @content_template)

I tried to access it in an ERB template, as "Using Ruby variable in Javascript (In App View)" says I can do, so I tried:

<script type="text/javascript" charset="utf-8">
 var url = <%= @print_url %>;
</script>

However, Chrome's console gives me this error:

Uncaught SyntaxError: Invalid flags supplied to RegExp constructor '13'

As you can see, it gets interpreted by JavaScript as a regular expression because it is not evaluated as a string. Why isn't Ruby evaluating this as a string? I don't understand why the example in the other link works but why mine does not.

• C3roe: "Why isn't ruby evaluating this as a string?" – the context of the error is not Ruby, it’s JavaScript. And how do we write text literals in JS again ...?
• Donato: @CBroe you are right, but at the time, I was expecting that value to be already parsed as string before it was rendered in javascript.
• C3roe: Whether or not ruby parsed it as a string doesn’t matter here – JavaScript is the context that you are introducing the value into here, and therefor you have to treat it according to the syntax rules of that context.

Answer 1

You need to use quotes around the value:

<script type="text/javascript" charset="utf-8">
 var url = '<%= @print_url %>';
</script>