Parsing javascript arrays and adding and deleting json elements_javascript skills

3 ways to delete arrays in JavaScript
1, use the shift() method
shift: delete the first item of the original array and return the value of the deleted element ;If the array is empty, it returns undefined
var chaomao=[1,2,3,4,5]
var chaomao.shift()//Get 1
alert(chaomao)//[2, 3,4,5]

2, use pop() method
pop: delete the last item of the original array and return the value of the deleted element; if the array is empty, return undefined
var chaomao=[1 ,2,3,4,5]
var chaomao.pop()//Get 5
alert(chaomao)//[1,2,3,4]
The previous method can only operate on arrays At the beginning and end, the middle item cannot be operated. If you want to operate the middle item, use the splice method

3. Use the splice method
This method is very powerful and can add, delete, and replace any item in the array

Modification operation:
var chaomao=[1,2,3,4,5]
chaomao.splice(2,1,8,9)
alert(chaomao)//1,2,8,9,4,5
The first parameter is the array position to be operated on, the second parameter is the number of array items behind the operation position, and the third parameter What follows is that the replaced content
example means: starting from position 2 of the array chaomao (that is, the item with a value of 3, the array subscript starts from 0), the item after position 2, Replace with 8,9
If you change the second parameter to 2, that is chaomao.splice(2,2,8,9), that is to say, the two items after position 2 are replaced with 8,9, and print The result is that the two items 1, 2, 8, 9, 5, 3 and 4 have been replaced
It should be noted here that the number of replaced items does not have to be equal to the number of replaced items, 1 Items can be replaced with 3 items, and 5 items can also be replaced with 2 items. Based on this principle, we use this method to add and delete arrays

Delete operation:
var chaomao=[1,2,3,4,5]
chaomao.splice(2,1)
alert (chaomao)//1,2,4,5
In the above example, the 1 item after position 2 in chaomao is replaced with empty, because there is no content after it. As you can see, the 3 item is deleted.

Add operation:
var chaomao=[1,2,3,4,5]
chaomao.splice(2,0,8,9)
alert(chaomao)//1,2,8,9,3,4,5
In the above example, replace the 0 item after position 2 in chaomao with 8,9, which is equivalent to adding two Item
In fact, deletion and addition operations are just two derivatives of the splice modification method
Javasscript method of deleting objects
To delete object elements in js, use the delete operator
We Let’s take a look at an example

Copy the code The code is as follows:

var p ={
"name": "chaomao",
"age":45,
"sex":"male"
};
delete p.name
for(var i in p){
console.log(i);//Output age, sex, name item has been deleted
}

Method to add json elements

Copy code The code is as follows:

var json = {}; // Skip if json is already defined
json[text] = value;
json.text2 = value2; // At this time, text2 must meet the variable name standard, otherwise it must be assigned in array