how to find specific value in mongodb code example

Example 1: mongodb find field based on variable

var name = req.params.name;
var value = req.params.value;
var query = {};
query[name] = value;
collection.findOne(query, function (err, item) { ... });

Example 2: mongo console find by id

db.collection.find({_id:ObjectId('5e208c18d598b806c869ca37')}).pretty()