How can I see all properties (including inherited) in nodejs? - node.js

Question

When working with nodejs, I like to use console.log to see what data is available in an object.
However, this doesn't work with inherited properties:
var Person = function () {};
Person.prototype.name = "anonymous";
var p = new Person();
console.log(['p', p]); // [ 'p', {} ]
// This doesn't even give me a hint that it's inherited from Person!
console.log(['typeof p', typeof p]); // [ 'typeof p', 'object' ]
console.log(['p.name', p.name]); // "anonymous"
Given an object, how can view all the properties I can access?

Answer 1

If your purpose is just for debugging, you can check the __proto__ object:
function Person() {};
Person.prototype.name = "abc";
Person.prototype.smallObj = {
name: "abc"
};
Person.prototype.deepObj = {
one: {
two: {
three: {
four: "4"
}
}
}
};
var p = new Person();
console.log(p);
// Person {}
console.log(p.__proto__);
/*
Person {
name: 'abc',
smallObj: { name: 'abc' },
deepObj: { one: { two: [Object] } }
}
*/
var util = require("util");
console.log(util.inspect(p.__proto__, {depth: null}));
/*
Person {
name: 'abc',
smallObj: { name: 'abc' },
deepObj: { one: { two: { three: { four: '4' } } } }
}
*/
On the last one, using util.inspect() with the depth option will allow you to look further into deeply nested objects.

Answer 2

You are assigning property to constructor function Person. It does not share properties with instances. You need to add property to Person's prototype:
Person.prototype.name = "anonymous";
To find out if your object inherited from Person you can do:
p instanceof Person; // true
You can print out all of an object's enumerable properties by performing the following:
for (var key in p) {
console.log(key);
}

Answer 3

Use Object.getOwnPropertyNames() to get all properties that belong to an object:
console.log(Object.getOwnPropertyNames(Person))
// [ 'length', 'name', 'arguments', 'caller', 'prototype' ]
console.log(Object.getOwnPropertyNames(Object))
// ['length','name','arguments','caller','prototype','keys','create', 'defineProperty','defineProperties','freeze','getPrototypeOf','setPrototypeOf','getOwnPropertyDescriptor','getOwnPropertyNames','is','isExtensible','isFrozen','isSealed','preventExtensions','seal','getOwnPropertySymbols','deliverChangeRecords','getNotifier','observe','unobserve','assign' ]
Also you can combine Object.getOwnPropertyNames() with walking up the prototype chain:
var getAllProperties = function (object) {
var properties = []
do {
Object.getOwnPropertyNames(object).forEach((prop) => {
if (!~properties.indexOf(prop)) {
properties.push(prop)
}
})
} while (object = Object.getPrototypeOf(object))
return properties
}