These days, it doesn't happen too often that a song strikes me as perfect. Good? Yes. Great? Maybe. Perfect? Don't delude yourself. In the whole of 2017, only Jarvis Cocker's "The Other Side", Peter Perrett's "Hard To Say No" and Destroyer's "Sky's Grey" would qualify.
And Morrissey:
"Jacky's Only Happy When She's Up On The Stage" is perfect, which is all the more impressive because the sound quality is understandably poor (in fact, it pains me to imagine how good it will sound in late November).
The song itself is vicious pop music, with Morrissey relishing every moment. There is no mystery as to who Jacky is, and if you have any doubts, the final chant will leave no room for imagination. Frankly, it doesn't get much better than this.