Object.constructor###
object.constructor
a = new Array(1,2,3); // Create an object
a.constructor == Array // Evaluates to true
Object.create()###
Object.create(proto); Object.create(proto, descriptors)
// Create an object that has own properties x and y and inherits property z
var p = Object.create({z:0}, {
x: { value: 1, writable: false, enumerable:true, configurable: true},
y: { value: 2, writable: false, enumerable:true, configurable: true},
});
Object.defineProperties()###
Object.defineProperties(o, descriptors)
// Add read-only properties x and y to a newly-created object
var p = Object.defineProperties({}, {
x: { value: 0, writable: false, enumerable:true, configurable: true},
y: { value: 1, writable: false, enumerable:true, configurable: true},
});
Object.defineProperty()
Object.defineProperty(o, name, desc)
function constant(o, n, v) { // Define a constant o.n with value v
Object.defineProperty(o, n, { value: v, writable: false
enumerable: true, configurable:false});
}
Object.getOwnPropertyDescriptor()
Object.getOwnPropertyDescriptor(o, name)
The descriptor for a data property looks like this:
{
value: /* any JavaScript value */,
writable: /* true or false */,
enumerable: /* true or false */,
configurable: /* true or false */
}
The descriptor for an accessor property looks like this:
{
get: /* function or undefined: replaces the property value */,
set: /* function or undefined: replaces the writable attribute */,
enumerable: /* true or false */,
configurable: /* true or false */
}
Object.getOwnPropertyNames()
Object.getOwnPropertyNames(o)
Object.getOwnPropertyNames([]) // => ["length"]: "length" is non-enumerable
Object.getPrototypeOf()
Object.getPrototypeOf(o)
var p = {}; // An ordinary object
Object.getPrototypeOf(p) // => Object.prototype
var o = Object.create(p) // An object that inherits from p
Object.getPrototypeOf(o) // => p
Object.hasOwnProperty()###
object.hasOwnProperty(propname)
var o = new Object(); // Create an object
o.x = 3.14; // Define a noninherited local property
o.hasOwnProperty("x"); // Returns true: x is a local property of o
o.hasOwnProperty("y"); // Returns false: o doesn't have a property y
o.hasOwnProperty("toString"); // Returns false: toString property is inherited
Object.isPrototypeOf()###
object.isPrototypeOf(o)
var o = new Object(); // Create an object
Object.prototype.isPrototypeOf(o) // true: o is an object
Function.prototype.isPrototypeOf(o.toString); // true: toString is a function
Array.prototype.isPrototypeOf([1,2,3]); // true: [1,2,3] is an array
// Here is a way to perform a similar test
(o.constructor == Object); // true: o was created with Object() constructor
(o.toString.constructor == Function); // true: o.toString is a function
// Prototype objects themselves have prototypes. The following call
// returns true, showing that function objects inherit properties
// from Function.prototype and also from Object.prototype.
Object.prototype.isPrototypeOf(Function.prototype);
Object.keys()###
Object.keys(o)
Object.keys({x:1, y:2}) // => ["x", "y"]
Object.propertyIsEnumerable()###
object.propertyIsEnumerable(propname)
var o = new Object(); // Create an object
o.x = 3.14; // Define a property
o.propertyIsEnumerable("x"); // true: property x is local and enumerable
o.propertyIsEnumerable("y"); // false: o doesn't have a property y
o.propertyIsEnumerable("toString"); // false: toString property is inherited
Object.prototype.propertyIsEnumerable("toString"); // false: nonenumerable