Declare two syntax for objects

1.1 grammar

The first kind;let obj = { name: "frank".age: 18}; The second;let obj = new Object({ name: "frank"}); Anonymous objects:console.log({'name':"frank".age:18})
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Note:

{foo : 'a'}
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Is not the object

1.2 Writing method of attribute name

  1. The key name (attribute name) is always a string, not an identifier, and can contain any character
  2. Quotation marks can be omitted, and only identifiers (except full numbers) can be used after omission.
  3. Even if the quotes are omitted, the key is a string.
  4. You must enclose quotation marks when there are Spaces and special characters.
  5. There are no numeric keys or numeric subscripts because the browser automatically converts numbers to strings.

1.3 Variables as attribute names

If you want to use the value of the variable as the attribute name, enclose the attribute name with []

let a = 'xxx'
let obj = {[a] : 111}
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contrast

  1. Attribute names without [] are automatically changed to strings
  2. [] is evaluated as a variable
  3. If the value is not a string, it tries to change to a string

2 How do I delete an object attribute

2.1 grammar

deleteObj. XXX ordelete obj['xxx']
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2.2 Checking whether an attribute is an attribute of the object

Methods a'name' in obj // false cannot distinguish whether the property is its own or common to the stereotypeMethod 2 obj. HasOwnProperty ('name') // false
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2.3 pay attention to

obj.xxx === undefinedCan't judge'xxx'Is an attribute of obj, if:'xxx' in obj && obj.xxx === undefined
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Example:

var obj = {}
var obj2 = {x: undefined}
obj.x === undefined // true
obj2.x === undefined // true
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3. How do I view the properties of an object

3.1 Viewing all properties of the Object

Object.keys(obj) / / check the keys
Object.values(obj) / / check values
Object.entries(obj) // check keys and values
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3.2 Viewing the Object itself + Common Properties

console.dir(obj) // View its own properties as a directory
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3.3 Determine whether an attribute is self-contained or common

'name' in obj // Cannot determine whether this attribute is a property of its own or a shared property
obj,hasOwnProperty('name') // true represents a property of its own
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3.4 Two Methods to View Attribute Values

Parenthesis syntax: obj['key'[obj. Key]Copy the code

Pay attention to

obj[key] // the value of the variable key is indeterminate
obj[console.log('name')] // undefined because.log returns undefined
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4 How can I modify or add attributes of an object

4.1 Direct assignment

let obj = {name: 'frank'} change: obj. Name = obj'an'
obj['name'] = 'an'
obj['na' + 'me'] = 'an'Or:let key = 'name'
obj[key] = 'an'
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4.2 Batch Assignment

Object.assign(obj,{age: 18.gender: 'man'})
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4.3 Modifying Common Attributes

  1. Common attributes cannot be modified or added by themselves
  2. To modify or add properties on the stereotype
obj.__proto__.toString = 'xxx' / / do not recommend
Object.prototype.toString = 'xxx'

obj.__proto__ === window.Object.prototype
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4.4 Modifying the Prototype

obj.__proto__ = null / / do not recommend
let obj = Object.create(common) // Attributes are on the prototype
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