What is the difference between JavaScript's object literals and object that appears to be named when console logged?

Question

I have noticed there are times when I console.log an object, I get the object literal and sometimes its seems what is console.logged is prefixed with a name.

For example, If I console.log an object before sending it to the server I get:

{id: 18, date: "2017-09-13T21:59:59.999Z"...etc}

but when I console the same log returned as a promise from a server call, I get:

Resource {id: 18, date: "2017-09-13T21:59:59.999Z"...etc}

What causes this differences? and What are the differences between what seems to be two different representations of an object?

The latter is a class instance. You can check this with myObject instanceof Resource. — Andrei Nemes
– Andrei Nemes, Commented Sep 14, 2017 at 16:32

Patrick Kunka · Accepted Answer · 2017-09-14 19:22:28Z

1

The latter is an instance of a named class:

class Resource {
   constructor() {
      this.id = ...;
      this.date = ...;
   }
}

Or a named constructor:

function Resource() {
  this.id = ...;
  this.date = ...;
}

In both cases, the class or constructor in instantiated with the new keyword, but class is the newer ES6 syntax.

console.log(new Resource())

Your first example is simply a plain object with no constructor.

edited Sep 14, 2017 at 19:22

answered Sep 14, 2017 at 16:37

Patrick Kunka

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Jonas Wilms · Accepted Answer · 2017-09-14 16:30:57Z

1

They have a constructor property, that does not point to Object, but to Ressource in that case.

answered Sep 14, 2017 at 16:30

Jonas Wilms

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Olga · Accepted Answer · 2017-09-14 16:34:37Z

1

The console is giving you hints, it doesn't always log stuff as is.

For example:

var Cat = function (name) {
    this.name = name;
}

var paws = new Cat('paws');
console.log(paws);

will act similar to Resource in your example. The console is hinting at the constructor.

answered Sep 14, 2017 at 16:34

Olga

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