Use underscore.js template engine with Mustache-style template tags (including escaping) instead of concatenation

template.js

_.template(
  '[{{{ shortcodeString }}} url="{{{ url }}}" width="{{{ width }}}" height="{{{ height }}}"]',
  {'shortcodeString': 'test', 
   'url': 'http://example.com', 
   'width': '100', 
   'height': '200'
   }, {
   interpolate: /\{\{([\s\S]+?)\}\}/g, 
   escape: /\{\{\{([\s\S]+?)\}\}\}/g}
);