Diff Comparison Operation In Moment.js

This is Duplicate of this question. I don't know how to compare the diff. For example if the diff equal to greater than 14 days then the text box should be red. if 7 to 13 days it

Solution 1:

This is not a valid condition: else if(7 < diff =< 9), it shoud be else if(diff > 7 && diff <= 9)