Transformers in Disguise (Robbers' Thread)
Node.js v10.9.0, Arnauld



o=&gt;[...o].sort(n=&gt;16&amp;(j+=13),j=9).join``


Try it online!

This outputs this particular permutation of itself when using Node's current sorting algorithm:

&amp;`nij.9=j.,)r31n=+(=ooj`[o.o.)1.s](&gt;=6&gt;t


An insightful comment by l4m2 gave me a headstart, but I had to write a brute-forcer to figure out which permutation of digits gives the correct output...