When 'grunt build' is run all the scripts are merged and minified. This produces a 'undefined' error because one of the scripts is missing a ; semicolon to properly end the script.
Basically we need such a option: https://github.com/gruntjs/grunt-contrib-concat#separator Which does not exist in grunt-contrib-uglify.
This error only appears if you have to do 'grunt build'.
I don't know what your task build does, but assume it's something close to "running everything", like $ grunt by itself would do...
@jakerella is right, uglify doesn't feature a separator as concat does.
I would use concat to concatenate the scripts with a separator of your choice (concat lets you do that) and then use uglify to minify whatever script concat concatenated.
uglifytask, I'm not sure what you can do about it other than either add the semicolons manually or use theconcattask in addition to theuglifytask. - Jordan Kasper