JSON array objects and object arrays

1. Brief Introduction to JSON
In terms of structure, all data can be divided into three types:
The first type is scalar (scalar), which is a separate string or number (numbers), such as the word "Beijing.
The second type is sequence (sequence), that is, several related data are listed in a certain order, also called array or list, for example, "Beijing, tokyo ".
The third type is mapping, that is, a name/value pair (name/value), that is, the data has a name and a value corresponding to it, this is also called hash or dictionary, for example, "capital: Beijing ".
JSON (JavaScript Object Notation) is a lightweight data exchange format. Its rules are simple and Interesting Of:
1) Separate the parallel data with commas.
2) The ing is represented by a colon.
3) The set (array) of the parallel data is represented by square brackets.
4) The ing set (object) is represented by braces.
According to this rule, we can understand the following:
1. an array is created with "[]", an object is created with "{}", and JSON is basically an array or object created with [] or, otherwise, a normal string is meaningless;
2. Elements of arrays and objects are separated by commas;
3. Inside the object, the (attribute) names and values are separated by ":" and must be separated by ":". Attribute names or values cannot exist separately;
4. objects and arrays can be nested, that is, an element in an array can be an object or an array. Likewise, the value of an attribute in an object can be an object or an array.
Ii. Examples
1.
VaR China = {Beijing: {name: "Beijing", Area: "16000", Haidian: {name: "Haidian District "}},
Shanghai: {name: "Shanghai", Area: "10000", Minhang: {name: "Minhang District "}}};
Alert (China. Beijing. Haidian. Name );
Alert (China. Shanghai. Minhang. Name );
"Haidian District" and "Minhang District" are displayed respectively ".
2.
VaR ourcountry = [["Beijing"], ["Shanghai"], ["Hefei", "Wuhu", "Bengbu"];
Alert (ourcountry [2] [1]);
Wuhu City is displayed ".
3.
VaR Zhongguo = {provinces: [{name: "Beijing", cities: [{name: "Beijing", quxian: ["Haidian District", "Chaoyang District", "Dongcheng District ", "Xicheng district"]},
{Name: "Anhui Province", cities: [{name: "Wuhu City", quxian: ["fanchang county", "Wuhu County", "Nanling County", "Sanshan district"]}, {name: "Hefei", quxian: ["Feixi county", "Shushan district", "luyang district"]},
"Hubei Province"
]};
VaR STR = "China: {\ n ";
For (VAR I = 0; I <Zhongguo. Provinces. length; I ++)
{
If (Zhongguo. Provinces . Cities! = NULL)
{
STR + = Zhongguo. Provinces . Name + "{";
For (var j = 0; j <Zhongguo. Provinces . Cities. length; j ++)
{
If (Zhongguo. Provinces . Cities [J]! = NULL)
{
STR + = Zhongguo. Provinces . Cities [J]. Name + "{";
For (var k = 0; k <Zhongguo. Provinces . Cities [J]. quxian. length; k ++)
{
STR + = Zhongguo. Provinces . Cities [J]. quxian [k];
If (K! = Zhongguo. Provinces . Cities [J]. quxian. Length-1)
{
STR + = ",";
}
}
STR + = "}";
}
}
STR + = "} \ n ";
}
}
STR + = "}";
Alert (STR );
"
China :{
Beijing {Haidian District, Chaoyang district, Dongcheng District, Xicheng district }}
{Wuhu City {fanchang County, Wuhu County, Nanling County, Sanshan district} Hefei {Feixi County, Shushan district, luyang district }}
}
".
Iii. Application of JSON in Ajax
The client can easily submit data to the server through the address bar or post. However, after the server completes data processing, it is difficult to return the computing result information to the client, especially when the data volume is large. At this time, the data format becomes the key. According to a specific format, data can be easily assembled and then parsed conveniently. JSON is a good strategy. On the server side, a string is assembled in JSON format and returned to the client. How do I parse the client? Generally, there are two policies (the names of these two policies are self-Assigned Names, which are not necessarily reasonable, but the idea should be correct ):
1. Direct Parsing
VaR JSON = eval ('+ Result + ')');
Through the above expression, the JSON string that the server returns to the client is parsed into a JSON (Format) object named "JSON" and passed "JSON. or "JSON.
2. Indirect Parsing
VaR JSON = "r =" + result;
Eval (JSON );
Of course the above lineCodeCan be merged into: eval ("r =" + result );
Through the above calculation, you can also parse the JSON string returned by the server to the client into a JSON (Format) object, but the object name is "r ", through "R. or "R.
Summary: JSON is a simple data exchange format. It can replace XML to allow flexible data exchange between servers.
Iv. arrays and objects in Javascript
In JavaScript, the data format created by [] is usually called an array, and what is created by {} is called an object.
There is an array A = [,], and an object A = {,}, run alert (A [1]), in both cases, the running results are the same! This means that the data set can be represented by arrays or objects. Which one should it be used?
In fact, arrays represent the set of ordered data, and objects represent the set of unordered data. If the order of data is important, use an array. Otherwise, use an object.
Of course, another difference between an array and an object is that the data in the array does not have a "name" and the data in the object has a "name ). But the problem is that there are manyProgramming LanguageIs called associativearray. The data in this array is named. For example, in Javascript, you can define an object as follows:
VaR A = {"city": "Beijing", "area": 16800, Interesting , "Population": 1600 };
However, it can also be defined as an associated array:
VaR A = new array ();
A ["city"] = "Beijing ";
A ["area"] = 16800;
A ["Population"] = 1600;
In this way, it seems that there is no difference between arrays and collections. Actually, no. In JavaScript, an associated array is an object, and an object is an associated array. There is a big difference between an array created in the second method and an array created in the [] method. In the "array" created in the second method, you can also use the ". city to get "Beijing", ". population "to get" 1600 ", but it is different from the object created in the first method. The first method defines a without the Length attribute, second, the second method defines a as yes, but the value is 0. The difference is still visible. To be specific, I'm afraid I have to look at some of the underlying implementation code.

When the JSON value returned by Eval is returned, error: Invalid label abstract is displayed. We often return a value in JSON format on the server side, which can be directly used as a complete object in the script, however, many new users usually encounter an error message: Invalid label, which is often annoying because the JSON format is correct but prompts an error. If you encounter this problem, please take a look at the content of this article!

We often return a value in JSON format on the server side, which can be directly used as a complete object in the script. However, many new users usually encounter an error message: Invalid label, this problem is often distressing, because the correct JSON format is prompted with an error.

assume that you return a JSON string from the server:
run in eval mode in the script:
the following message is displayed: error: invalid label
In fact, our JSON format is not incorrect, but in Eval, enclose your JSON value in brackets ():
var result = eval ("(" + O. responsetext + ")"); help001