2022.2.12

• Insert delete array elements

  // It can only be inserted and deleted from the tail 
  arr.push(0);//push, write in , That is, insert the element in parentheses in the last position of the array , Numbers without quotation marks , Characters with quotation marks 
  arr.pop();//pop, Delete , Delete the last element in the array , There is no need to fill in the brackets ,pop You can only delete one by one 
  

  // It can only be inserted and deleted from the head 
  arr.shift(1);// Insert... From the head , Be similar to push
  arr.unshift();// Remove... From the head , Be similar to pop
  

• Sort

  arr.sort();//sort The function is to sort , There is no need to enter a value in brackets 
  

• Element inversion

  arr.reverse();// Arrange all the elements in the array in the reverse order of the current order 
  

• Link string

  arr.concat(arr1);// In brackets , If it is an array variable, fill in the variable name directly , If it's a hashed element , Then add brackets ; notes ：concat The array is not modified , Only a new array is returned 
  

• Connector

  arr.join('-');// Fill in the brackets with what you want to connect , Just a style , Output is as follows ：
  arr.join('-')
  '0-7-5-2-3-1-6-4-9'// notes ： Quotation marks must be added in brackets 
  

• Multidimensional arrays

  arr = [[x,x,···],[x,x,···],[x,x,···]];// Multidimensional array is the nesting of arrays 
  console.log(arr[1][1]);// Use the subscript of multidimensional array to get 
  

5、 object

• Several key value pairs

  'use strict';
      let person = {
        
          name:"zhangsan",
          age:3,
          email:"[email protected]",
          score:0
      }// Define an object , Its content “name”、“age” Etc. are the properties of the object , The type of attribute is string type 
  

• Object Assignment

  person.name = "lisi";// Assignment of elements in the object 
  person.age;// Output the value of the corresponding attribute of the object 
  

• If you use a nonexistent object, there will be no error , Will be output “undefined”

• Delete properties dynamically

  delete person.name;// Whether it exists or not, it will return a true, When the deleted attribute is output again undefined
  

• Add properties dynamically

  person.sex = "man";// Directly add violence 
  

• Determine whether the property value is in the object

  'score' in person;// The format is xxx attribute  in xxx object 
  true
  'toString' in person;// inheritance , The properties of the parent class can also be found in this object 
  true
  

• Determine whether a property is owned by the object itself

  person.hasOwnProperty('age');