ember source file is collapsed in browser devtools

I am developing a web application using Ember. When i was going to debug my code in chrome, One of .js file of my source code is collapsed { which consist of 2052 lines }. When i press the "pretty print" button which is visible in left bottom corner, the source code get expanded. Actually it opens as a new file with the name as :formatted.js Even i can view it in expanded view i can not place debug points inside that file. Later what i found was, by deleting a one function inside the file i can fix this problem. Please let me know whether this problem is due to the length of the file or something else. Tell me a way to fix this. Thanks a lot.