//list of the entries in the headings drop box
//the keys give the corresponding elements in the rows
var leg = {
aa: " ... ",
...
};

##

Error while executing command: executeScript: An unknown server-side error occurred while processing the command.: {"errorMessage":"Return statements are only valid inside functions",

##

##

my ($val, $type) = $js->eval_in_page('(function() {return JSON.stringify(leg);})()');
print "val: $val, type: $type\n";

##

##

Error while executing command: executeScript: An unknown server-side error occurred while processing the command.: {"errorMessage":"Can't find variable: leg","request":{"headers":{"Accept":"application/json","Connection":"TE, close","Content-Length":"74","Content-Type":"application/json; charset=utf-8","Host":"127.0.0.1:8910","TE":"deflate,gzip;q=0.3","User-Agent":"libwww-perl/6.15"},"httpVersion":"1.1","method":"POST","post":"{\"args\":[],\"script\":\"return (function() {return JSON.stringify(leg);})()\"}","url":"/execute","urlParsed":{"anchor":"","query":"","file":"execute","directory":"/","path":"/execute","relative":"/execute","port":"","host":"","password":"","user":"","userInfo":"","authority":"","protocol":"","source":"/execute","queryKey":{},"chunks":["execute"]},"urlOriginal":"/session/95efd1d0-8ea9-11e9-b043-85beee600173/execute"}} at C:/strawberry/perl/site/lib/Selenium/Remote/Driver.pm line 389.