I really like the idea of using handle bars to create HTML templated content for emails etc as a much neater way of separating presentation from logic and enabling us to store the templates in a simple database and inject data as a separate process.

Anyway, I am starting to use the more advanced features like each and helpers and I got the error above when trying to run my template.

It turns out that it wasn't a HandleBars error as such, I had a helper like this:

Handlebars.RegisterHelper("FormatNumber", (writer, context, parameters) => {

and this was called from a template like this:

"{{FormatNumber AverageScore}}"

and on first inspection, I didn't understand what I was soing wrong and why I got such a weird error (rather than simply missing or malformed content. Of course, after looking carefully, the line of code that was actually erroring was:


And it turns out that since parameters are dynamic, I realised that AverageScore was not the correct name of the data parameter but it should have been Average.Without it being a valid piece of data, the helper simply injected the string "AverageScore" which, naturally, would not covert to a decimal.

Fun times!