JavaScript Object Functions cheat sheet Part 3

JavaScript Object Functions Part 3

Object.isExtensible()

Object.isExtensible() determines whether an object can have new properties added to it

Syntax

  Object.isExtensible(obj)

Example

  const obj = {}

  Object.isExtensible(obj) // true

  Object.preventExtensions(obj)

  Object.isExtensible(obj) // false

Object.isFrozen()

Object.isFrozen() determines if an object is frozen

Syntax

  Object.isFrozen(obj)

Example

  const obj = {}

  Object.isFrozen(obj) // false

  Object.freeze(obj)

  Object.isFrozen(obj) // true

Object.isSealed()

Object.isSealed() determines if an object is sealed

Syntax

  Object.isSealed(obj)

Example

  const obj = {}

  Object.isSealed(obj) // false

  Object.seal(obj)

  Object.isSealed(obj) // true

Object.keys()

Object.keys() returns array of object's enumerable property names

Syntax

  Object.keys(obj)

Example

  Object.keys({ a: 1, b: 2 }) // [ "a", "b" ]

Object.preventExtensions()

Object.preventExtensions() prevents new properties from being added to an object

Syntax

  Object.preventExtensions(obj)

Example

  const obj = {

    a: 1

  }

  Object.preventExtensions(obj)

  Object.defineProperty(obj, 'b', {

    value: 2

  }) // Error: Can't define property 

  //"b": Object is not extensible

  

Object.prototype.hasOwnProperty()

Object.prototype.hasOwnProperty() returns boolean indicating whether object has the specified property

Syntax

  obj.hasOwnProperty(prop)

Example

  const obj = {

    a: 1

  }

  obj.hasOwnProperty('a') // true

  obj.hasOwnProperty('b') // false

  

Object.prototype.isPrototypeOf()

Object.prototype.isPrototypeOf() checks if object exists in another object's prototype chain

Syntax

  prototypeObj.isPrototypeOf(object)

Example

  const proto = {

    a: 1

  }

  const obj = Object.create(proto)

  proto.isPrototypeOf(obj) // true

Object.prototype.propertyIsEnumerable()

Object.prototype.propertyIsEnumerable() checks whether the specified property is enumerable and is the object's own property.

Syntax

  obj.propertyIsEnumerable(prop)

Example

  const obj = {

    a: 1

  }

  const arr = ['a']

  obj.propertyIsEnumerable('a') // true

  arr.propertyIsEnumerable(0) // true

  arr.propertyIsEnumerable('length') // false

  

Object.prototype.toString()

Object.prototype.toString() returns a string representing the object

Syntax

  obj.toString()

Example

  const obj = {}

  obj.toString() // "[object Object]"

  const arr = ['a', 'b']

  arr.toString() // "a,b"

Object.seal()

Object.seal() prevents new properties from being added and marks all existing properties as non-configurable

Syntax

  Object.seal(obj)

Example

  const obj = {

    a: 1

  }

  Object.seal(obj)

  obj.a = 2 // { a: 2 }

  obj.b = 3 // error in strict mode

  delete obj.a // error in strict mode

  

Object.values()

Object.values() returns array of object's own enumerable property values

Syntax

  Object.values(obj)

Example

  Object.values({ a: 1, b: 'a'}) // [ 1, "a" ]

Thanks for reading... 👏👏

JavaScript Object Functions cheat sheet Part 2