Mongoose - Save array of strings

var schema = new Schema({
  name:    String,
  binary:  Buffer,
  living:  Boolean,
  updated: { type: Date, default: Date.now },
  age:     { type: Number, min: 18, max: 65 },
  mixed:   Schema.Types.Mixed,
  _someId: Schema.Types.ObjectId,
  decimal: Schema.Types.Decimal128,
  array: [],
  ofString: [String],
  ofNumber: [Number],
  ofDates: [Date],
  ofBuffer: [Buffer],
  ofBoolean: [Boolean],
  ofMixed: [Schema.Types.Mixed],
  ofObjectId: [Schema.Types.ObjectId],
  ofArrays: [[]],
  ofArrayOfNumbers: [[Number]],
  nested: {
    stuff: { type: String, lowercase: true, trim: true }
  },
  map: Map,
  mapOfString: {
    type: Map,
    of: String
  }
})

// example use

var Thing = mongoose.model('Thing', schema);

var m = new Thing;
m.name = 'Statue of Liberty';
m.age = 125;
m.updated = new Date;
m.binary = Buffer.alloc(0);
m.living = false;
m.mixed = { any: { thing: 'i want' } };
m.markModified('mixed');
m._someId = new mongoose.Types.ObjectId;
m.array.push(1);
m.ofString.push("strings!");
m.ofNumber.unshift(1,2,3,4);
m.ofDates.addToSet(new Date);
m.ofBuffer.pop();
m.ofMixed = [1, [], 'three', { four: 5 }];
m.nested.stuff = 'good';
m.map = new Map([['key', 'value']]);
m.save(callback);

Write up from my comment:

The way to specify an array of strings in mongoose is like so:

var personSchema = new mongoose.Schema({
tags: [{
    type: String
}]

However, the problem here is most-likely to do with Postman as it is sending the 'array' as a string. You can check this by checking the type of req.body.tags like so:

console.log(typeof req.body.tags)

If this returns a String, make sure to set the content-type in Postman to JSON as seen in this screenshot rather than the default 'form-data' option.

Try changing the schema to

var personSchema = new mongoose.Schema({
  tags: [{type: String}]
});

or you can use Mixed type

var personSchema = new mongoose.Schema({
  tags: mongoose.Schema.Types.Mixed
});

EDIT

i think the problem is with assignment. Use:

person.tags.push("string to push");

1. On Schema:
   ( Since you have mentioned in the problem that it is an array of strings )

var personSchema = new mongoose.Schema({
  tags:{
     type:[String],
     required: true
  }
}); 

2. On Postman:
   

{
  "tags": ["css", "javascript", "mongoose", "node"]
}

3. On MongoDB

{
  "tags":["css", "javascript", "mongoose", "node"]
}

Similarly, you can create other types of primitive arrays and document arrays in the mongoose schema as:

({
  toys: [ToySchema],
  buffers: [Buffer],
  strings: [String],
  numbers: [Number]
  // ... etc
});