How to rewrite the javascript template string -

i'm trying modify code https://github.com/airblade/chartjs-ror/blob/master/vendor/assets/javascripts/chart.js

i need rewrite original string template tooltiptemplate: "<%=datasetlabel%> - <%= value %>", want add if else condition it.

but template string complex

how rewrite following logic ?

my rough logic is

if ( %value > 0) {%datasetlabel - %value} else {     %datasetlabel - "empty value" } 

% means variable in above logic

i guess can (untested code, idea):

yourtemplate: "<%if (value > 0){%>"    + "<%= datasetlabel - value %>"          + "<%}%>"                                + "<%else {%>"                           + "<%= datasetlabel - \"empty value\"%>" + "<%}%>"