handlebars-helper-x.js

  // for detailed comments and demo, see my SO answer here http://stackoverflow.com/questions/8853396/logical-operator-in-a-handlebars-js-if-conditional/21915381#21915381
  
  /* a helper to execute an IF statement with any expression
    USAGE:
   -- Yes you NEED to properly escape the string literals, or just alternate single and double quotes 
   -- to access any global function or property you should use window.functionName() instead of just functionName()
   -- this example assumes you passed this context to your handlebars template( {name: 'Sam', age: '20' } ), notice age is a string, just for so I can demo parseInt later
   <p>
     {{#xif " name == 'Sam' && age === '12' " }}
       BOOM
     {{else}}
       BAMM
     {{/xif}}
   </p>
   */

  Handlebars.registerHelper("xif", function (expression, options) {
    return Handlebars.helpers["x"].apply(this, [expression, options]) ? options.fn(this) : options.inverse(this);
  });

  /* a helper to execute javascript expressions
   USAGE:
   -- Yes you NEED to properly escape the string literals or just alternate single and double quotes 
   -- to access any global function or property you should use window.functionName() instead of just functionName(), notice how I had to use window.parseInt() instead of parseInt()
   -- this example assumes you passed this context to your handlebars template( {name: 'Sam', age: '20' } )
   <p>Url: {{x " \"hi\" + name + \", \" + window.location.href + \" <---- this is your href,\" + " your Age is:" + window.parseInt(this.age, 10) "}}</p>
   OUTPUT:
   <p>Url: hi Sam, http://example.com <---- this is your href, your Age is: 20</p>
  */
 Handlebars.registerHelper("x", function(expression, options) {
   var result;

   // you can change the context, or merge it with options.data, options.hash
   var context = this;

   // yup, i use 'with' here to expose the context's properties as block variables
   // you don't need to do {{x 'this.age + 2'}}
   // but you can also do {{x 'age + 2'}}
   // HOWEVER including an UNINITIALIZED var in a expression will return undefined as the result.
   with(context) {
     result = (function() {
       try {
         return eval(expression);
       } catch (e) {
         console.warn('•Expression: {{x \'' + expression + '\'}}\n•JS-Error: ', e, '\n•Context: ', context);
       }
     }).call(context); // to make eval's lexical this=context
   }
   return result;
});