Parsing error: Unexpected token .. when using grunt build

I'm fairly new to the linux webapp development scheme but there was a readme attached with the project that the previous team left me.

It said I have to call 1)Sudo npm install 2) bower install 3)grunt build/grunt server.

firstly, my bower.json is empty with the exception of { "name": "webapp", "dependencies": { "roslib": "~0.15.0" } }

and secondly when i call grunt build i get the error error Parsing error: Unexpected token let I also get the same error with the tokens '<' and 'ILLEGAL'

via Marian Daniel