library(microbenchmark)

microbenchmark( as.integer( names( skJSONraw [1] ) ) 
              , as.integer( names( skJSONraw       ) [1] ) 
              , as.integer( names( skJSONraw       ) [[1]] )   
#              ,  as.integer( names( skJSONraw       )       ) [[1]] 
              )


Unit: microseconds
                               expr   min     lq median     uq    max
1 as.integer(names(skJSONraw)[[1]]) 1.478 1.6310 1.7330 1.7965 54.106
2   as.integer(names(skJSONraw)[1]) 1.943 2.0490 2.1115 2.1825 35.575
3   as.integer(names(skJSONraw[1])) 2.394 2.5185 2.6045 2.7620 45.988