I create a toClient() method on my models where I do this. It's also a good place to rename/remove other attributes you don't want to send to the client:
Schema.method('toClient', function() {
var obj = this.toObject();
//Rename fields
obj.id = obj._id;
delete obj._id;
return obj;
});
Given you're using Mongoose, you can use 'virtuals', which are essentially fake fields that Mongoose creates. They're not stored in the DB, they just get populated at run time:
// Duplicate the ID field.
Schema.virtual('id').get(function(){
return this._id.toHexString();
});
// Ensure virtual fields are serialised.
Schema.set('toJSON', {
virtuals: true
});
Any time toJSON is called on the Model you create from this Schema, it will include an 'id' field that matches the _id field Mongo generates. Likewise you can set the behaviour for toObject in the same way.
See:
You can abstract this into a BaseSchema all your models then extend/invoke to keep the logic in one place. I wrote the above while creating an Ember/Node/Mongoose app, since Ember really prefers to have an 'id' field to work with.