Json

1–json以键值对形式存储数据
—key:键 ;
—value:值;
—key:一般都为字符串,命名见名知意,代表value的含义
—value:可以为任意数据类型

eg:

var aJson = {

name:”sunjie”,

“age”:”18”,

“sex”:”女”

};

–1.1–json取值:

console.log(aJson[“sex”]);

打印结果:

女

–1.2–json赋值
—如果json数剧中存在key值,那么直接改变key对应的value值
—如果json数据中不存在key值,那么在json中添加一对键值对

aJson[“name”] = “lily”;

console.log(aJson[“name”]);

aJson[“weight”] = “65”;

var height = “height”;

aJson[height] = “165”;

console.log(aJson);

打印结果为:

lilyObject  age: "18"   height: "165"   name: "lily"  sex: "女"   weight: "65"

2–json遍历
—json遍历时,i代表key值,aJson代表value值

eg:

for (var i in aJaon ) {

console.log( i + “:” + aJson[i]);

}

打印结果为:

name:lilyage:18sex:女weight:65height:165

3–数组遍历
–3.1–用for in
—数组遍历用for in;
—数组遍历用for in 时,i代表的是数组的下标,arr代表的是数组

var arr = [1,3,4,6,7,10,18];

for (var i in arr ) {

console.log(i + “:” + arr[i]);

打印结果为:

0:11:32:43:64:75:106:18

–3.2–用for循环
—用for循环遍历数组,i = 0代表数组下标是0开始,下标小于数组长度,arr[i]代表数组中的每一个数字
for (var i = 0; i < arr.length; i++) {
console.log(arr[i]);
}
打印结果为:

134671018

4–json练习

var aJson = {

a: [{

“abc”: 123,

“bc”: 34,

“cd”: 34

}, {

“abc”: 456,

“bdc”: 123,

“mn”: 78

}, {

“abc”: 789,

“xyz”: 123

}]

};

–要求:
–4.1–打印每个abc对应的value值:

code:

var json = aJson[“a”];

for (var i in json) {

console.log(json[i][“abc”]);

}

printout:

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