Checks for plain objects

checks-for-plain-objects.md

(Node.js v0.11〜)

               typeof=o       protoToStr     proto=ObjProto proto=null     ctor=Obj       ctor=null      protoCtor=Obj  protoCtor=null 
-- strict plain object --
(1)            true           true           true           false          true           false          true           false          
(2)            true           true           true           false          true           false          true           false          
(3)            true           true           true           false          true           false          true           false          
-- wider plain object --
(4)            true           true           false          true           false          false          false          false          
(5)            true           true           false          false          true           false          true           false          
-- non plain object --
(6)            true           false          false          false          false          false          false          false          
(7)            false          false          false          false          false          false          false          false          
(8)            false          false          false          false          false          false          false          false          
(9)            false          false          false          false          false          false          false          false          
(10)           false          false          false          false          false          false          false          false          
(11)           true           false          false          false          false          false          false          false          
(12)           true           false          false          false          false          false          false          false          
(13)           true           false          false          false          false          false          false          false          
(14)           true           false          false          false          false          false          false          false          
(15)           true           false          false          false          false          false          false          false          
(16)           true           false          false          false          false          false          false          false          
(17)           false          false          false          false          false          false          false          false          
(18)           false          false          false          false          false          false          false          false          
(19)           false          false          false          false          false          false          false          false          
(20)           true           true           false          false          false          false          false          false          
(21)           true           true           false          false          false          false          false          false          
-- by JSON.parse --
(22)           true           true           true           false          true           false          true           false          
(23)           true           true           true           false          true           false          true           false          
(24)           true           true           true           false          true           false          true           false          
(25)           true           true           true           false          true           false          true           false          
(26)           true           true           true           false          true           false          true           false          
(27)           true           true           true           false          true           false          true           false          
(28)           true           true           true           false          true           false          true           false          
(29)           true           true           true           false          true           false          false          false          
(30)           true           true           true           false          false          false          true           false          
(31)           true           true           true           false          false          false          true           false          
(32)           true           true           true           false          false          false          true           false          
(33)           true           true           true           false          false          false          true           false          
(34)           true           true           true           false          false          false          true           false          
-- fiddle .__proto__ and .constructor
(35)           true           true           true           false          false          true           true           true           
(36)           true           true           false          true           false          false          false          false          
(37)           true           true           true           false          false          true           false          true      

(Node.js 〜v0.10)

               typeof=o       protoToStr     proto=ObjProto proto=null     ctor=Obj       ctor=null      protoCtor=Obj  protoCtor=null 
-- strict plain object --
(1)            true           true           true           false          true           false          true           false          
(2)            true           true           true           false          true           false          true           false          
(3)            true           true           true           false          true           false          true           false          
-- wider plain object --
(4)            true           true           false          true           false          false          false          false          
(5)            true           true           false          false          true           false          true           false          
-- non plain object --
(6)            true           false          false          false          false          false          false          false          
(7)            false          false          *Error*        *Error*        false          false          false          false          
(8)            false          false          *Error*        *Error*        false          false          false          false          
(9)            false          false          *Error*        *Error*        false          false          false          false          
(10)           false          false          *Error*        *Error*        false          false          false          false          
(11)           true           false          false          false          false          false          false          false          
(12)           true           false          false          false          false          false          false          false          
(13)           true           false          false          false          false          false          false          false          
(14)           true           false          false          false          false          false          false          false          
(15)           true           false          false          false          false          false          false          false          
(16)           true           false          false          false          false          false          false          false          
(18)           false          false          false          false          false          false          false          false          
(19)           false          false          false          false          false          false          false          false          
(20)           true           true           false          false          false          false          false          false          
(21)           true           true           false          false          false          false          false          false          
-- by JSON.parse --
(22)           true           true           true           false          true           false          true           false          
(23)           true           true           true           false          true           false          true           false          
(24)           true           true           true           false          true           false          true           false          
(25)           true           true           false          false          true           false          true           false          
(26)           true           true           false          false          true           false          true           false          
(27)           true           true           false          false          true           false          true           false          
(28)           true           true           false          false          true           false          true           false          
(29)           true           true           false          true           false          false          false          false          
(30)           true           true           true           false          false          false          true           false          
(31)           true           true           true           false          false          false          true           false          
(32)           true           true           true           false          false          false          true           false          
(33)           true           true           true           false          false          false          true           false          
(34)           true           true           true           false          false          false          true           false          
-- fiddle .__proto__ and .constructor
(35)           true           true           true           false          false          true           true           true           
(36)           true           true           false          true           false          false          false          false          
(37)           true           true           true           false          false          true           false          true       

source-code.md

'use strict';

var padRight = require('@fav/text.pad-right');

var funcs = [
  ['typeof=o', function(v) {
    return (typeof v === 'object');
  }],
  ['protoToStr', function(v) {
    return Object.prototype.toString.call(v) === '[object Object]';
  }],
  ['proto=ObjProto', function(v) {
    try {
      return (v != null) && (Object.getPrototypeOf(v) === Object.prototype);
    } catch (e) {
      return '*Error*';
    }
  }],
  ['proto=null', function(v) {
    try {
      return (v != null) && (Object.getPrototypeOf(v) === null);
    } catch (e) {
      return '*Error*';
    }
  }],
  ['ctor=Obj', function(v) {
    return (v != null) && (v.constructor === Object);
  }],
  ['ctor=null', function(v) {
    return (v != null) && (v.constructor === null);
  }],
  ['protoCtor=Obj', function(v) {
    return (v != null) && (v.__proto__ != null) && (v.__proto__.constructor === Object);
  }],
  ['protoCtor=null', function(v) {
    return (v != null) && (v.__proto__ != null) && (v.constructor === null);
  }],
];

var colWidth = 15;

function header() {
  var str = funcs.map(function(fn) {
    return fn[0];
  }).reduce(function(s, r) {
    return s + padRight(r, colWidth);
  }, padRight('', colWidth));
  console.log(str);
}

function test(n, v) {
  var str = funcs.map(function(fn) {
    try {
      return fn[1](v);
    } catch (e) {
      return '*Error*';
    }
  }).reduce(function(s, r) {
    return s + padRight('' + r, colWidth);
  }, padRight('(' + n + ')', colWidth));
  console.log(str);
}

header();
console.log('-- strict plain object --');
test(1, {});
test(2, { foo: 'bar' });
test(3, Object.create(Object.prototype));

console.log('-- wider plain object --');
test(4, Object.create(null));
test(5, Object.create({}));

console.log('-- non plain object --');
test(6, null);
test(7, true);
test(8, 0);
test(9, 123);
test(10, 'abc');
test(11, new Date(0));
test(12, new Number(123));
test(13, new String('abc'));
test(14, []);
test(15, ['foo', 'bar']);
test(16, new Array());
//test(17, Symbol('foo'));
test(18, function() {});
test(19, function Foo() {});
test(20, new function() {});
test(21, new function Bar() {});

console.log('-- by JSON.parse --');
test(22, JSON.parse('{}'));
test(23, JSON.parse('{"foo":"bar"}'));
test(24, JSON.parse('{"hasOwnProperty":"bar"}'));

test(25, JSON.parse('{"__proto__":{}}'));
test(26, JSON.parse('{"__proto__":{"polluted":1}}'));
test(27, JSON.parse('{"__proto__":{"__proto__":{}}}'));
test(28, JSON.parse('{"__proto__":{"__proto__":{"polluted":1}}}'));
test(29, JSON.parse('{"__proto__":null}'));

test(30, JSON.parse('{"constructor":{"prototype":{}}}'));
test(31, JSON.parse('{"constructor":{"prototype":{"polluted":1}}}'));
test(32, JSON.parse('{"constructor":{"prototype":{"__proto__":{}}}}'));
test(33, JSON.parse('{"constructor":{"prototype":{"constructor":{"prototype":{"polluted":1}}}}}'));
test(34, JSON.parse('{"constructor":{"prototype":null}}'));

console.log('-- fiddle .__proto__ and .constructor')
var a = {};
a.constructor = null;
test(35, a);

a = {};
a.__proto__ = null;
test(36, a);

a = {};
a.__proto__.constructor = null;
test(37, a);

% node
Welcome to Node.js v15.5.0.
Type ".help" for more information.
> function A() {}
undefined
> var a = new A();
undefined
> a
A {}
> a instanceof A
true
> a.constructor = Object
[Function: Object]
> a
{ constructor: [Function: Object] }
> a instanceof A
true
> a.__proto__ = Object.prototype
[Object: null prototype] {}
> a
{ constructor: [Function: Object] }
> a instanceof A
false
> a = new A();
A {}
> a.__proto__ = Object.prototype
[Object: null prototype] {}
> a instanceof A
false
>