Mongoose virtual games, 'this' is an empty object

Question

ok, I'm new to mongoose and trying to figure out how to use virtual properties. This is an example of the code I tested.

var mongoose = require('mongoose'); var Schema = mongoose.Schema; var objSchema = new Schema({ created: {type: Number, default: Date.now()}, }); objSchema.virtual('hour').get(()=>{ //console.log(this); var d = new Date(this.created); return d.getHours(); }); var obj = mongoose.model('obj', objSchema); var o = new obj(); o.toObject({virtuals: true}); console.log(o.created); console.log(o.hour); 

so I expect the log will be something like:

 1457087841956 2 

but the way out

 1457087841956 NaN 

and when I log 'this' at the beginning of the virtual receiver, it prints {}. What am I doing wrong?

Answer 1

The problem is the arrow function used in the virtual function, the same problem can be found here anonymous ES6 function and circuit methods , the reason is this function Lexical arrow function

To solve this problem, change your codes below:

 objSchema.virtual('hour').get(function(){ console.log(this.created); var d = new Date(this.created); return d.getHours(); });