A brief discussion on the stringify function, toJosn function and parse function in JSON_json

JSON.stringify function (JavaScript)

Syntax: JSON.stringify(value [, replacer] [, space])

Convert a JavaScript value to a JavaScript Object Notation (Json) string.

Copy code The code is as follows:

value
Required. The JavaScript value to convert (usually an object or array).
replacer
Optional. The function or array used to convert the result.
If replacer is a function, JSON.stringify will call the function, passing in the key and value of each member. Use the return value instead of the original value. If this function returns undefined, the member is excluded. The key of the root object is an empty string: "".
If replacer is an array, only members with key values ​​in the array are converted. Members are converted in the same order as the keys in the array. When the value argument is also an array, the replacer array is ignored.
space
Optional. Adds indentation, spaces, and newlines to the return value JSON text to make it easier to read.
If space is omitted, the return value text will be generated without any extra spaces.
If space is a number, the return value text is indented by the specified number of spaces at each level. If space is greater than 10, the text is indented by 10 spaces.
If space is a non-empty string (such as " "), the return value text is indented at each level by characters in the string.
If space is a string longer than 10 characters, the first 10 characters are used.

If value has a toJSON method, the JSON.stringify function will use the return value of that method. If the return value of the toJSON method is undefined, the member is not converted. This enables the object to determine its own JSON representation.

Values ​​that do not have a JSON representation, such as undefined, will not be converted. In the object, these values ​​are discarded. In the array, these values ​​are replaced with null.

Execution order

During the serialization process, if the value parameter corresponds to the toJSON method, JSON.stringify will first call the toJSON method. If the method does not exist, the original value is used. Next, if the replacer parameter is supplied, that value (either the original value or the toJSON return value) is replaced with the return value of the replacer parameter. Finally, spaces are added to the value based on the optional space parameter to produce the final JSON text.

This example uses JSON.stringify to convert a contact object to JSON text. Define the memberfilter array to convert only the surname and phone members. Omit the firstname member.

Copy code The code is as follows:

var contact = new Object();
contact.firstname = "Jesper";
contact.surname = "Aaberg";
contact.phone = ["555-0100", "555-0120"];
var memberfilter = new Array();
memberfilter[0] = "surname";
memberfilter[1] = "phone";
var jsonText = JSON.stringify(contact, memberfilter, "t");
document.write(jsonText);
// Output:
// { "surname": "Aaberg", "phone": [ "555-0100", "555-0120" ] }

toJSON method (Date) (JavaScript)

Syntax: objectname.toJSON()

objectname

Required. Object that needs to be JSON serialized.

The toJSON method is a built-in member of the Date JavaScript object. It returns an ISO-formatted date string in the UTC time zone (represented by the suffix Z).

The following example uses the toJSON method to serialize uppercase string member values. The toJSON method is called when calling JSON.stringify.

Copy code The code is as follows:

JavaScript
var contact = new Object();
contact.firstname = "Jesper";
contact.surname = "Aaberg";
contact.phone = ["555-0100", "555-0120"];
contact.toJSON = function(key)
{
var replacement = new Object();
for (var val in this)
{
If (typeof (this[val]) === 'string')
            replacement[val] = this[val].toUpperCase();
        else
            replacement[val] = this[val]
}
Return replacement;
};
var jsonText = JSON.stringify(contact);
/* The value of jsonText is:
'{"firstname":"JESPER","surname":"AABERG","phone":["555-0100","555-0120"]}'
*/

JSON.parse function (JavaScript)

Convert JavaScript Object Notation (JSON) string to object

Syntax: JSON.parse(text [, reviver])

Copy code The code is as follows:

text
Required. A valid JSON string.
reviver
Optional. A function that converts the result. This function will be called for each member of the object. If a member contains nested objects, the nested objects are converted before the parent object. For each member, the following happens:
If reviver returns a valid value, the member value is replaced with the converted value.
If the reviver returns the same value it received, the member value is not modified.
If reviver returns null or undefined, the member is removed.

The following example uses JSON.parse to convert a JSON string into an object.

Copy code The code is as follows:

var jsontext = '{"firstname":"Jesper","surname":"Aaberg","phone":["555-0100","555-0120"]}';
var contact = JSON.parse(jsontext);
document.write(contact.surname ", " contact.firstname);
// Output: Aaberg, Jesper

The following example demonstrates how to use JSON.stringify to convert an array into a JSON string, and then use JSON.parse to convert the string back into an array.

Copy code The code is as follows:

var arr = ["a", "b", "c"];
var str = JSON.stringify(arr);
document.write(str);
document.write ("
");
var newArr = JSON.parse(str);
while (newArr.length > 0) {
Document.write(newArr.pop() "
");
}
// Output:
// ["a","b","c"]
// c
// b
// a