_.extend is undefined in js code generated from coffeescript

Question

I have some CoffeeScript code, which is not written by me. I have compiled it to Javascript via a provided Grunt script and manually via coffee --compile my_single_file.coffee . In both cases, the following snippet is generated to loop over a list:

_ref1 = this.baseMap;
for (_j = 0, _len1 = _ref1.length; _j < _len1; _j++) {
  c = _ref1[_j];
  o = _.extend(c); 

If I try to use the generated file in my page, the underscore in the last line is undefined. I guess I'm missing some includes, compile flags, ... but I found no hint what it might be. Any hint what I might be doing wrong?

Answer 1

Maybe it depends on something else? Looks like underscore.js although the extend method requires two arguments.