代码如下：

let WordsMetaSchema = new mongoose.Schema({
	//总文档数
	total: {type: Number, default: 0},
	//标签对应总文档数
	labels: {
		厌恶: {type: Number, default: 0},
		同情: {type: Number, default: 0},
		喜欢: {type: Number, default: 0},
		怨恨: {type: Number, default: 0},
		悲伤: {type: Number, default: 0},
		焦虑: {type: Number, default: 0},
		愤怒: {type: Number, default: 0}
	}
});
	    
WordsMetaSchema.statics = {
	getTotal$: function() {
		return Promise.resolve(this.findOne({}).toObject().total);
	},
	add$: function(labels)  {
		let ctx = this;
		let incs = {$inc: {total: 1}}
		labels.forEach( l => {
			incs.$inc['labels.'+l] = 1;
		});
		console.log(incs)
		return this.update({}, incs);
	}
};
	    
let WordsMeta = mongoose.model('words_meta', WordsMetaSchema);
	    
mongoose.connect('mongodb://localhost:27017/emo');
	    
WordsMeta.add$(['厌恶', '愤怒']).then( x => {
	console.log(x)
	mongoose.disconnect();
});

输出结果如下：

{ '$inc': { total: 1, 'labels.厌恶': 1, 'labels.愤怒': 1 } }
{ ok: 1, nModified: 0, n: 0 }

但是查看数据库，根本没有这个words_meta collection