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JSON value acquisition and traversal [json]

2022-07-21 18:35:00 【Java code evolution ing】

JSON Value acquisition and traversal

obtain JSON data

JSON object . Key name
JSON object [“ Key name ”]
- Be careful : When using this method, the key name should be ""( Double quotes ) Include , It's in string form
Array objects [ Indexes ]
- If JSON Object is in array , Then use this method

For example, to understand :

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>JSON Value acquisition </title>
		<script> //1.  Define the basic format  var person = {
      "name":" Zhang San ","age":23,"gender":true}; var name = person.name; alert(name); var name = person["name"]; alert(name); //2.  Nesting format : {} -> [] ,  This means JSON Object [] Array  var persons = {
       "persons" : [ {
      "name":" Zhang San ","age":23,"gender":true}, {
      "name":" Li Si ","age":23,"gender":true} ] } // This way is to use the key to get the value first ,  But after getting the value, the value is an array ,  There are objects in the array ,  So we get the array  // After a certain value in, you can still use the corresponding key to obtain the value  var name1 = persons.persons[1].name; alert(name1); //3.  Nesting format : [] -> {} ,  Here, it means that the array is nested JSON object  var ps = [ {
      "name":" Li Si ","age":23,"gender":true}, {
      "name":" Li Si ","age":23,"gender":true}, {
      "name":" Li Si ","age":23,"gender":true}, {
      "name":" Li Si ","age":23,"gender":true} ] // In this way, we directly locate an object through the index of the array ,  Then get the corresponding value through the key  var name2 = ps[1].name; alert(name2); </script>
	</head>
	<body>
	</body>
</html>

JSON Data traversal :

Use for in loop :

For example, to understand :

var person = {
    "name":" Zhang San ","age":23,"gender":true};


for (let key in person) {
    
    alert(key);
}

Be careful : Here is the will person The keys in the object are all traversed , Each iteration will temporarily store the key of the object to a temporary variable key in
- Obtained after traversal key The value of is of string type , So we can only get the corresponding value through person[key] The way , They can't be used person.key The way
  - Because at this time key It's string type , If at this time key by "name", So obviously if we are person."name" It's just wrong , And if it is person[“name”] It means to get the name person Of JSON The corresponding key name of the object is "name" Value

If it is JSON Object in array , Then we add an outer layer when traversing for Circulation is enough :( as follows :)

//3.  Nesting format : [] -> {} ,  Here, it means that the array is nested JSON object 
var ps = [
    {
    "name":" Zhang San ","age":23,"gender":true},
    {
    "name":" Li Si ","age":23,"gender":true},
    {
    "name":" Wang Wu ","age":23,"gender":true},
    {
    "name":" Li Si ","age":23,"gender":true}
]

for (var i = 0; i < ps.length; i++) {
    
    var p = ps[i];
    for (let key in p) {
    
        alert(key + ":" + p[key])
    }
}

This method is actually the same as the previous one , Actually traversal JSON Objects are always used for let in loop , Just because the elements in the array are one by one in this traversal process JSON object , So we need to use a common for Loop through the array

Add :

for let in Loop traversal JSON Data is like us Java Strengthening in for loop (foreach) equally , Each time the traversed data is stored in a temporary variable , It's just different for let in Loop traversal JSON Array is traversed to the key every time , So it's what you will traverse every time JSON The value of the key in the data is stored in a temporary variable

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