squares and curlies

replacements.js

var tmplExpressions = [
  {
    expression: /\[\[([^\]]*)\]\]/g,
    replace: "{{$1}}"
  },
  {
    expression: /\$\[([^\]]*)\]/g, 
    replace: "${$1}"
  }
];

_.each(tmplExpressions, function(expr) {
  str = str.replace(expr.expression, expr.replace);
});