js> dis(class c{x=2;})
flags: CONSTRUCTOR
loc     op
-----   --
00000:  functionthis                    # THIS
00001:  setlocal 0                      # THIS
00005:  pop                             #
main:
00006:  getgname ".initializers"        # .initializers
00011:  zero                            # .initializers 0
00012:  callelem                        # .initializers[0]
00013:  getlocal 0                      # .initializers[0] this
00017:  call-ignores-rv 0               # .initializers[0](...)
00020:  pop                             #
00021:  retrval                         #

Source notes:
 ofs line    pc  delta desc     args
---- ---- ----- ------ -------- ------
  0:    2    21 [  21] xdelta
  1:    2    21 [   0] colspan 5
  3:    2    21 [   0] breakpoint