javascript - NodeJS MongoDB adapter interprets string as literal instead of value -

i have following code:

var keyexp = 'experiencecat' + req.param('category'); user.native(function(err,collection) {     collection.find({'_id':{$in:usersarray}},{fields:{'name':1,'avatar':1,'fbid':1,'country':1,keyexp:1}}).toarray(function (err,userprofiles)     {         res.send(userprofiles);     }); }); 

the problem instead of changing keyexp current value (which should "experiencecat0" example) it's trying find column name "keyexp" of course doesn't exist.

how should code able read correct column based on req.param('category') parameter?

here's how should today:

var fields = {'name':1,'avatar':1,'fbid':1,'country':1}; fields['experiencecat' + req.param('category')] = 1; user.native(function(err,collection){     collection.find({'_id':{$in:usersarray}},{fields:fields}).toarray(function (err,userprofiles)     {         res.send(userprofiles);     }); }); 

with es6 you'll able express in more concise way:

var keyexp = 'experiencecat' + req.param('category'); user.native(function(err,collection){     collection.find( ... ,'fbid':1,'country':1,[keyexp]:1}}).toarray(function (err,userprofiles)                                                ^^^^^^^^     {         res.send(userprofiles);     }); });