Convert Json objects and strings to each other. Detailed introduction to json data splicing and JSON usage.

JSON (JavaScript Object Notation) is a lightweight data exchange format. It is based on a subset of ECMAScript. JSON uses a completely language-independent text format, but also uses conventions similar to the C language family (including C, C++, C#, Java, JavaScript, Perl, Python, etc.). These properties make JSON an ideal data exchange language. It is easy for humans to read and write, and it is also easy for machines to parse and generate (generally used to increase network transmission rates).

1. Convert JSON string to JSON object: eval() and JSON.parse

eg- json string:

var data = '{ "name": "dran", "sex": "man" }';
var obj = eval("("+data+")"); 或者
var obj = JSON.parse(data)；

Then, you can read it like this: alert(obj.name + obj. sex);

Tips: Why do you need to add ("("+data+")"); to eval?

The reason lies in: the problem of eval itself. Since json starts and ends with "{}", it will be processed as a statement block in JS, so it must be forced to be converted into an expression.

The purpose of adding parentheses is to force the eval function to convert the expression in the parentheses into an object when processing JavaScript code, rather than executing it as a statement. For example, if the object literal {} is not added with outer brackets, then eval will recognize the braces as the start and end marks of the JavaScript code block, and {} will be considered to execute an empty statement

2. Convert JSON object to JSON string: obj.toJSONString() or global method JSON.stringify(obj) (obj represents json object)

eg-json对象: var obj = { "name": "dran", "sex": "man" };
var jstring = JSON.stringify(obj) ;// 建议用这个
var jstring = obj.toJSONString(); //toJSONString()不是js原生的方法，需要引入相应的库或自己定义后才能用 (不习惯用)

Then, you can read it like this: alert(jstring );

Note:

Currently, Firefox, Opera, IE8 and above also provide local JSON support. Among them, the functions provided by the JSON interpreter are: JSON.parse, JSON.stringify. For browsers that do not provide native JSON support, the script json2.js can be introduced to implement the JSON conversion function. The json2.js script can be downloaded from https://github.com/douglascrockford/JSON-js/blob/master/json2.js

When AJAX implements front-end and back-end data interaction, the JSON data format is usually used. For JSON, there are strict code specifications. Once there is a problem with the format, the corresponding effect cannot be displayed, and an error is not reported on the console.

Additional: ajax reads json data and splicing displays:

json file:

{
"first":[
{"name":"张三","sex":"男","like":["吃饭","睡觉","打豆豆"]},
{"name":"李四","sex":"男"},
{"name":"王武","sex":"男"},
{"name":"李梅","sex":"女"},
],
"second":[
{"name":"上海大学","area":"上海"},
{"name":"武汉大学","area":"武汉"},
{"name":"北京大学","area":"北京"},
{"name":"山东大学","area":"山东"},
]
}

html and ajax code

1. Use for loop

$.ajax({
url : "ceshi.json",
type : "POST",
dataType :"text", //浏览器把json文件当作文本文件 不然读取不出来 权宜之策就改成了text， 因为测试， json文件格式正确书写
success: function(data) {
var dataJson = eval("("+data+")"); // 将json字符串数据解析成对象
var arr1 = dataJson.first;
var arr2 = dataJson.second;
//一栏显示 用for循环完成数组解析
for(var i = 0; i<arr1.length; i++){
for(var j = 0; j<arr2.length; j++){
var str=&#39;<div style="display:block">&#39;+
&#39;<div>姓名：&#39;+arr1[i].name+&#39; 性别：&#39;+arr1[i].sex+&#39;</div>&#39;+
&#39;<div>学校:&#39;+arr2[j].name+&#39;</div>&#39;+
&#39;<div>地点:&#39;+arr2[j].area+&#39;</div>&#39;+
//&#39;<div>喜好:&#39;+arr1[i].like+&#39;</div>&#39;+ //全显示
//&#39;<div>喜好:&#39;+arr1[i].like[1]+&#39;</div>&#39;+ //单独设置
//&#39;<div>喜好:&#39;+arr1[i].like[0]+&#39;</div>&#39;+
&#39;</div>&#39;;
}
$(".result").append(str);
}
//分层显示
//var str = "";
// var str1 = "";
// if (arr1 != null) {
// for (var i = 0; i < arr1.length; i++) { //这里面都是创建并赋值
// str += "<span>" + arr1[i].name + "</span><span>" + arr1[i].sex + "</span><br>";
// }
// $(".result").html(str);
// }
// if (arr2 != null) {
// for (var j = 0; j < arr2.length; j++) {
// str1 += "<span>" + arr2[j].name + "</span><span>" + arr2[j].area+ "</span><br>";
// }
// $(".result2").html(str1);
// }
},
error:function(data){
alert("error");
}
})
<div class="result">frist:</div>
<div class="result2">second:</div>
for

2. Each loop uses $.each method to traverse the returned data date and insert it into class .result

JSON:

[
{"name":"张三","sex":"男","like":["吃饭","睡觉","打豆豆"]},
{"name":"李四","sex":"男"},
{"name":"王武","sex":"男"},
{"name":"李梅","sex":"女"},
]
$.ajax({
url : "ceshi.json",
type : "POST",
dataType :"text", //浏览器把json文件当作文本文件 不然读取不出来 权宜之策就改成了text， 因为测试， json文件格式正确书写
success: function(data) {
var dataJson = eval("("+data+")"); // 将json字符串数据解析成对象
//each循环 使用$.each方法遍历返回的数据date,插入到class为 .result中 i 表示索引 item 信息值 对象
$.each(dataJson,function(i,item){
var str=&#39;<div style="display:block">&#39;+
&#39;<div>姓名：&#39;+item.name+&#39; 性别：&#39;+item.sex+&#39;</div>&#39;+
&#39;<div>like:&#39;+item.like+&#39;</div>&#39;+
&#39;</div>&#39;;
$(".result").append(str);
})
},
error:function(data){
alert("error");
}
})
<div class="result"></div>
each

PS: For general js to generate json objects, you only need to replace the $.each() method with a for statement, and the others remain unchanged

JSON data usage method:

//json对象：
var jsonObj= {
"name":" 张三",
"sex":"男",
"age":26,
};
使用： jsonObj.name= "张三"
jsonObj.age= "26"
//json数组： []下标 从 0 开始
var jsonArr =[
{"name":"张三","sex":"男","like":["吃饭","睡觉","打豆豆"]},
{"name":"李四","sex":"男"},
{"name":"王武","sex":"男"},
]
使用： jsonArr[0].sex="男"
jsonArr[1].name="李四"
//多个数组： []下标 从 0 开始
var options = {
"city" :[
{
"name":"上海",
"area":"普陀区",
"option":"真北路",
"correct":"1"
},
{
"name":"石家庄",
"area":"河北",
"option":"在北方",
"correct":"2"
}],
"world":[
{
"title":"美国",
"content":"好莱坞大片 科幻"
},
{
"title":"中国",
"content":"爱我中华，虽远必诛"
}
]
};
options.city[0].area="普陀区"
options.world[1].content="爱我中华，虽远必诛