Json is a js object. ----- Simply put, JSON can convert a set of data represented in a JavaScript object to a string, and then it can be easily passed between functions, alternatively, the string is transmitted from the Web Client to the server in an asynchronous application. This string looks a bit odd (several examples will be seen later), but JavaScript can easily explain it, while Json is a js object.
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Simply put, JSON can convert a set of data represented in a JavaScript object to a string, and then it can be easily passed between functions, alternatively, the string is transmitted from the Web Client to the server in an asynchronous application. This string looks a bit odd (several examples will be seen later), but JavaScript can easily explain it, and JSON can represent a more complex structure than name/value pairs. For example, it can represent arrays and complex objects, not just a simple list of keys and values.
Simple JSON example
In the simplest form, you can use the following JSON to represent name/value pairs:
{"FirstName": "Brett "}
This example is very basic and actually takes more space than the equivalent plain text name/Value Pair:
FirstName = Brett
However, when multiple name/value pairs are concatenated, JSON will reflect its value. First, you can create records that contain multiple name/value pairs, for example:
{"FirstName": "Brett", "lastName": "McLaughlin", "email": "brett@newInstance.com "}
In terms of syntax, this is not a great advantage over name/value pairs, but JSON is easier to use and more readable in this case. For example, it explicitly indicates that the above three values are part of the same record; curly braces make these values have a certain relationship.
Array of Values
To represent a group of values, JSON not only improves readability, but also reduces complexity. For example, assume that you want to list a person's name. In XML, many start and end tags are required. If a typical name/value pair is used (like the name/value pair seen in the previous articles in this series ), you must either create a proprietary data format or change the key name to a person1-firstName.
If JSON is used, you only need to group multiple records with curly braces:
{"People ":[
{"FirstName": "Brett", "lastName": "McLaughlin", "email": "brett@newInstance.com "},
{"FirstName": "Jason", "lastName": "Hunter", "email": "jason@servlets.com "},
{"FirstName": "Elliotte", "lastName": "Harold", "email": "elharo@macfaq.com "}
]}
This is not hard to understand. In this example, there is only one variable named people. The value is an array containing three entries, each of which is a one-person record, including the name, last name, and email address. The preceding example demonstrates how to use parentheses to combine records into a value. Of course, you can use the same syntax to represent multiple values (each value contains multiple records ):
{"Programmers ":[
{"FirstName": "Brett", "lastName": "McLaughlin", "email": "brett@newInstance.com "},
{"FirstName": "Jason", "lastName": "Hunter", "email": "jason@servlets.com "},
{"FirstName": "Elliotte", "lastName": "Harold", "email": "elharo@macfaq.com "}
],
"Authors ":[
{"FirstName": "Isaac", "lastName": "Asimov", "genre": "science fiction "},
{"FirstName": "Tad", "lastName": "Williams", "genre": "fantasy "},
{"FirstName": "Frank", "lastName": "Peretti", "genre": "christian fiction "}
],
"Musicians ":[
{"FirstName": "Eric", "lastName": "Clapton", "instrument": "guitar "},
{"FirstName": "Sergei", "lastName": "Rachmaninoff", "instrument": "piano "}
]
}
It is worth noting that each value can contain multiple values. However, you should also note that the actual name/value pairs in the record can be different between different primary entries (programmers, authors, and musicians. JSON is completely dynamic and allows you to change the data representation mode in the middle of the JSON structure.
When processing data in JSON format, there are no predefined constraints to be observed. Therefore, in the same data structure, you can change the way data is represented, or even express the same thing in different ways.
Use JSON in JavaScript
After mastering the JSON format, it is easy to use it in JavaScript. JSON is a JavaScript native format, which means that no special API or toolkit is required to process JSON data in JavaScript.
Assign JSON data to a variable
For example, you can create a new JavaScript variable and assign a value to the JSON-format data string:
Var people =
{"Programmers ":[
{"FirstName": "Brett", "lastName": "McLaughlin", "email": "brett@newInstance.com "},
{"FirstName": "Jason", "lastName": "Hunter", "email": "jason@servlets.com "},
{"FirstName": "Elliotte", "lastName": "Harold", "email": "elharo@macfaq.com "}
],
"Authors ":[
{"FirstName": "Isaac", "lastName": "Asimov", "genre": "science fiction "},
{"FirstName": "Tad", "lastName": "Williams", "genre": "fantasy "},
{"FirstName": "Frank", "lastName": "Peretti", "genre": "christian fiction "}
],
"Musicians ":[
{"FirstName": "Eric", "lastName": "Clapton", "instrument": "guitar "},
{"FirstName": "Sergei", "lastName": "Rachmaninoff", "instrument": "piano "}
]
}
This is very simple; now people contains the data in JSON format as shown above. However, this is not enough, because the data access method does not seem obvious.
Access Data
Although it does not seem obvious, the long string above is actually an array. After you put this array into the JavaScript variable, you can easily access it. In fact, you only need to use the dot notation to represent array elements. Therefore, to access the first project name in the programmers list, you only need to use the following code in JavaScript:
People. programmers [0]. lastName;
Note that the array index starts from scratch. Therefore, this line of code first accesses the data in the people variable, then moves to the entry called programmers, and then to the first record ([0]). Finally, it accesses the value of the lastName key. The result is the string value "McLaughlin ".
The following are examples of using the same variable.
People. authors [1]. genre // Value is "fantasy"
People. musicians [3]. lastName // Undefined. This refers to the fourth entry,
And there isn' t one
People. programmers. [2]. firstName // Value is "Elliotte"
With this syntax, You can process data in any JSON format without using any additional JavaScript toolkit or API.
Modify JSON data
Just as you can access data with periods and parentheses, you can easily modify the data in the same way:
People. musicians [1]. lastName = "Your maninov ";
After converting a string to a JavaScript Object, you can modify the data in the variable as follows.
Convert back to string
Of course, if you cannot easily convert an object back to the text format mentioned in this article, all data modifications are of little value. In JavaScript, this conversion is also very simple:
String newJSONtext = people. toJSONString ();
That's all! Now you can obtain a text string that can be used anywhere. For example, you can use it as a request string in an Ajax application.
More importantly, any JavaScript Object can be converted to JSON text. It is not only applicable to variables that are originally assigned values using JSON strings. To convert an object named myObject, you only need to execute the same command:
String myObjectInJSON = myObject. toJSONString ();
This is the biggest difference between JSON and other data formats discussed in this series. If JSON is used, you only need to call a simple function to obtain formatted data and use it directly. For other data formats, the conversion between the original data and the formatted data is required. Even if you use an API like Document Object Model (which provides a function to convert your data structure to text), you also need to learn this API and use the Object of the API, instead of using native JavaScript objects and syntaxes.
The final conclusion is that if you want to process a large number of JavaScript objects, JSON is almost certainly a good choice, so that you can easily convert the data to a format that can be sent to the server-side program in the request.
Conclusion
This series has spent a lot of time discussing data formats, mainly because almost all asynchronous applications ultimately need to process data. If you have mastered various tools and technologies for sending and receiving all types of data and use them in the most appropriate way for each type of data, you will be more proficient in Ajax. On the basis of understanding XML and plain text, you can master JSON to process more complex data structures in JavaScript.
The next article in this series will discuss issues other than sending data and introduce how server programs receive and process data in JSON format. We also discuss how server programs can send back data in JSON format across scripts and server components, so that XML, plain text, and JSON requests and responses can be combined. This provides great flexibility and can be used in combination with almost any combination of these tools.
The above is a brief description of json content. For more information, please refer to other related articles in the first PHP community!
