Basic usage of the JS object CRUD

Conceptual understanding

Object definition:

• Unordered collection of data
• A collection of key-value pairs

 

Writing:

let {obj = 'name', 'bubu_sourire', 'age': 18 } 

let obj = new Object ({ 'name', 'bubu_sourire' }) 

console.log ({ 'name', 'bubu_sourire', 'age' : 18})

 

note:

• Keys are strings, not the identifier may comprise any character key
• Key quotes can be omitted, can only be written after the identifier is omitted, but even omitting quotation marks, there is still a key string .

 

About the property name (key / property) and property values ​​(value)

• Each key is the attribute name of the object
• Each attribute value is an object of value

 

Property name Example:

let obj = {
    1:'a',
    3.2:'b',
    1e2:true,
    1e-2:true,
    .234:true,
    0xFF:true    
}

Object.keys(obj) //可以得到obj所有的key

= ["1", "100", "255", "3.2", "0.01", "0.234"]

 

Variable names and attributes do make constant attribute name:

= per the let 'name' 

the let OBJ1 = {per: 'bubu_sourire'} // here attribute name is "per" 

the let obj2 = {[per]: 'bubu_sourire'} // here is the name attribute "name"

 

note:

• Without [] will automatically become the property name string
• Plus [] will be evaluated as a variable; If the value is not a string, the string will automatically become

 

Hidden property of an object

Common attributes prototype chain

 

Deletions object properties change search

Delete property

• Delete the obj property xxx

delete obj.xxx

delete obj.['xxx']

• Free property name

'xxx' in obj === false

• It contains the attribute name, but refers to the undefined

'xxx' in obj && obj.xxx = undefined

 

note:

obj.xxx === undefined can not be concluded 'xxx' whether obj property

 

 

 

View property

Two ways to view properties

obj.key // dot syntax 

obj. [ 'key'] // bracketed syntax 


obj. [key] // this is the key variable acquisition target value, the difference between this syntax (!!! easy to step on the pit, please be careful! !!)

 

note:

• obj.name equivalent to obj [ 'name'] (string).;
• obj.name not equivalent to obj [name] (variable value).;
• Here name is a string, not a variable.
• let name = 'bubu_sourire' => obj. [name] is equivalent to obj. [ 'frank']

 

Comparative Example

person.name

 

person[name]

 

 

 

 

• View all own property

Object.keys(obj)

• And their common attributes View

console.dir (obj)

Or printed out successively with Object.keys obj .__ proto__

• Judgment is itself a property or a total of

let obj = {'aaa':111}

obj.hasOwnProperty('aaa') //true
obj.hasOwnProperty('toString')  //false

 

Modifying or adding attributes

Direct assignment

obj = {name the let: 'AAA'} // name string 
obj.name = 'BBB' // name string 
obj [ 'name'] = 'CCC' 
obj [ 'Na' + 'Me'] = 'ddd' 

obj [name] = 'Eee' // !! undefined error !! name 


the let Key = 'name' 
obj. [Key] = 'ddd' // equivalent to obj [ 'name'] 

obj. Key = 'ddd' // !! !! obj.key error here is equivalent to obj. [ 'key']

 

Batch assignment

Object.assign(obj,{age:18,gender:'man'})

 

Modifying or adding common attributes

Can not by itself modify or increase common attributes, change can only change their own property

 

 

You can use obj .__ proto __. ToString = ' xxx' modify common attributes, but not recommended

 

 

Recommended Object.create

let obj = Object.create(common)

let obj = Object.create(common,{key1:{value:'value1'},key2:{value:'value2'}})