How to register JavaScript helpers with Handlebars.net

Question

How would we register these two JavaScript helpers in Handlebars.Net?

For Moment.js:

Handlebars.registerHelper("formatDate", function (datetime, format) {
    return moment(datetime).format(format);
});

For a java script calculation:

Handlebars.registerHelper("formatPercent", function (val1, limit) {
    return Math.ceil(100 * val1 / limit);
});m

Answer 1

The readme gives an example for how to write helpers:

Handlebars.RegisterHelper("link_to", (writer, context, parameters) => {
  writer.WriteSafeString("<a href='" + context.url + "'>" + context.text + "</a>");
});

string source = @"Click here: {{link_to}}";

var template = Handlebars.Compile(source);

var data = new {
    url = "https://github.com/rexm/handlebars.net",
    text = "Handlebars.Net"
};

var result = template(data);

/* Would render:
Click here: <a href='https://github.com/rexm/handlebars.net'>Handlebars.Net</a>
*/

The most important difference is in .NET, the helper doesn't return a value. Rather, you're given a reference to the TextWriter that is generating the template output. So your helper can write whatever it wants directly to the template via that writer. There is a .WriteSafeString() helper included to bypass the default encoding. Make sure your string is actually safe to not encode when you do that.

Answer 2

Found it. This example sheds some light https://gist.github.com/rexm/e1a045b9f76a48de642e

    Handlebars.RegisterHelper("formatDate", New HandlebarsHelper(Sub(w, c, p)
                                                                     w.WriteSafeString("moment(" + p(0) + ").format(" + p(1) + ");")
                                                                 End Sub))

    Handlebars.RegisterHelper("formatPercent", New HandlebarsHelper(Sub(w, c, p)
                                                                        If p(1) = 0 Then
                                                                            w.WriteSafeString("0")
                                                                        Else
                                                                            w.WriteSafeString("Math.ceil(" + 100 * p(0) / p(1) + ");")
                                                                        End If
                                                                    End Sub))