Object

Object is the most important data type in javascript, having a good understanding of how it works and how to change and use an object is largely beneficial for our development work.

There are several simple data types in javascript:

number
string
boolean
null
undefined

Other than these simple types everything else are objects.

An object is a container of properties.

Each property has a name and value. The property name can be any string including empty string, and value can any javascript value.

Object Literals

object literals are the name/value pairs between curly braces. E.G.

{
  foo: "bar"
}

{
  "foo": "bar"
}

• note: the quotes arround the key name is optional

Retrieval

There are two ways to retrieve value in an object.

foo.bar
foo["bar"]

Update

Like Retrieval there are two ways to update an object.

foo.bar = "123"
foo.["bar"] = "123"

Prototype

Each javascript is linked to a prototyp object. All the object literals is linked to Object.prototype object. You can also link prototype manually by using Object.create function.

let example = {
  foo: "this is foo",
  bar: "this is bar"
}

let another_example = Object.create(example)

console.log(another_example.foo)
> 'this is foo'
console.log(another_example.bar)
> 'this is bar'

Modifying the created object won't effect the prototype object:

another_example.foo = "another foo"

console.log(another_example.foo)
> 'another example'
console.log(another_example.__proto__.foo)
> 'this is foo'

Prototype object are dynamically binded to the objects that uses it as prototype object. Continue with the previous example.

example.foobar = "this is foobar"
console.log(another_example.foobar)
> 'this is foobar'

Inspection

The key word typeof can check the type of an object.

var example = {}
example.num1 = 1
typeof example.num1
> 'number'

Function hasOwnProperty can check if a object as certain property. This function does not look at the prototype chain.

var example = {}
example.num1 = 1
exmaple.string1 = "this is string"

var anotherObject = Object.create(example)
anotherObject.num1 = 2

console.log(example.hasOwnProperty("num1"))
> true
console.log(anotherObject.hasOwnProperty("num1"))
> true
console.log(example.hasOwnProperty("string1"))
> true
console.log(anotherObject.hasOwnProperty("string1"))
> false

Delete

The delete operator can be used to remove a property from an object.

console.log(anotherObject.num1)
> 2
delete anotherObject.num1
console.log(anotherObject.num1)
> 1

• Note: delete operator won't remove anything in the prototype chain.