People often joke about Javert’s haircut in the musical.
“Les cheveux des sous officiers et soldats seront attachés près de la tête et liés en queue, couverte d’un ruban de laine noire […]” –
Règlement concernant le service intérieur, la police et la discipline de l’infanterie du 24 juin 1792
“The hair of NCOs and privates shall be tied near the skull in a (pony)tail, covered with a ribbon of black wool […]” – Regulations concerning interior service, police and infantry discipline, 24th of June 1792.
(Interesting thing is to note that it was pretty much the same under the Ancient Regime, but the ribbon was made with black silk).
Javert simply has a military haircut according to French army regulations of the era.
I mean that might have been true when Javert started as a cop, but Valjean’s released from prison in 1815, and everything in Paris (in the musical) happens in 1832. By that point ponytail-length long hair for men was either an Eccentric Weirdo Counterculture thing, or a sign that you were die-hard refusing to let the Old Days go. It definitely wasn’t standard for cops and military men anymore.
Which doesn’t mean Javert’s hairstyle doesn’t make sense; it just means he’s that guy who wears the same haircut for forty years.
I think it’s pretty unlikely that Javert, whose “whole person was expressive of the man who spies and conceals himself”, would have a distinctive, memorable and pointedly anachronistic haircut. His whole raison d’être is enforcing the social order, and part of conforming to the social order is not having weird hair.
Besides, I doubt the 1790s were Javert’s favorite decade and one he wishes to commemorate with his hairstyle for the rest of his life. He was nine years old when the Bastille fell; he’s never had an adult haircut in pre-revolutionary France. His immediate association with queues would probably be the chaos of revolution, not the reassuring authoritarianism of the Ancien Régime. And if he did take it up it he wouldn’t just be retaining the styles of his youth for thirty years (totally plausible for Javert, fashion permitting), he’d be deliberately adopting an outdated hairstyle as a political statement. That seems to require much more thought than Javert would feel comfortable with.
Also I’m not entirely sure it’s an option? The one thing we do know about Javert’s hair in canon is that he’s sporting some serious bangs: “his hair concealed his forehead and fell over his eyebrows”. And while a ponytail with bangs is certainly a hairstyle that exists – I had it for most of my childhood – it doesn’t really seem to be on the table for men in the late 1700s. It’s a little hard to tell because everyone’s got a damn hat on all the time, but in contemporary paintings the choices seem to be either short hair with bangs, or a queue with all the hair pulled back from the forehead. I searched through a bunch of battle scenes and portraits and the only person I can find with something that might be a ponytail + bangs combo is baby Marshal Lobau here, who admittedly does look a bit Javert-y:
Of course, Musical Javerts often do have canonical ponytails, so, um… Maybe Quast!vert was in the Imperial Guard after all? Or maybe in the musical universe Napoleon never changed the regulations. (We know they didn’t abolish branding.)