prototype-in-js.md

JS中一些有关原型的问题

obj.hasOwnProperty('proto') === false

var o = {}

print('toString', o)
o.toString = true
print('toString', o)

print('__proto__', o)
o.__proto__ = true
print('__proto__', o)

function print(name, obj) {
  console.log(
    'name:', name,
    ',',
    'typeof:', typeof obj[name],
    ',',
    'hasOwnProperty:', Object.prototype.hasOwnProperty.call(obj, name)
  )
}

output:

name: toString , typeof: function , hasOwnProperty: false
name: toString , typeof: boolean , hasOwnProperty: true
name: __proto__ , typeof: object , hasOwnProperty: false
name: __proto__ , typeof: object , hasOwnProperty: false

Object.create(null)

var o = Object.create(null)

print('toString', o)
o.toString = true
print('toString', o)

print('__proto__', o)
o.__proto__ = true
print('__proto__', o)

function print(name, obj) {
  console.log(
    'name:', name,
    ',',
    'typeof:', typeof obj[name],
    ',',
    'hasOwnProperty:', Object.prototype.hasOwnProperty.call(obj, name)
  )
}

output:

name: toString , typeof: undefined , hasOwnProperty: false
name: toString , typeof: boolean , hasOwnProperty: true
name: __proto__ , typeof: undefined , hasOwnProperty: false
name: __proto__ , typeof: boolean , hasOwnProperty: true