js常见的转换

数组转化成字符串：

var  arr = [1,2,3,4,5];
var m = arr.join('-');
var n = arr.join('');
console.log(m);//1-2-3-4-5 使用-拼接数组元素
console.log((typeof m));//string
console.log(n);//12345
console.log((typeof n));//string

字符串转化成数组：

var str = 'ab+c+de';
var a = str.split('+'); // [ab, c, de]
console.log(typeof a);// object
var b = str.split(''); //[a, b, +, c, +, d, e]

json对象转化成json字符串

//使用JSON.stringify()
var json = {name: "zhangsan", age: 23, email: "[email protected]"};
var jsonStr = JSON.stringify(json);      
console.log(jsonStr);//"{"name":"zhangsan","age":23,"email":"[email protected]"}"

json字符串转化成json对象

//使用JSON.parse()函数
var jsonStr = '{"name":"zhangsan","age":23,"email":"[email protected]"}';
var json = JSON.parse(jsonStr);
console.log(json);//输出:Object {name: "zhangsan", age: 23, email: "[email protected]"}

数组转json串

var arr = [1,2,3, { a : 1 } ];
JSON.stringify( arr );

json字符串转数组

var jsonStr = '[1,2,3,{"a":1}]';
JSON.parse( jsonStr );

数组的长度

arr.length

字符串的长度

str.length

json对象的长度

//JavaScript里json格式的对象是没有length属性的，如果需要得到一个对象的具体有多少个属性，Object.keys方法就能派上用场了，Object.keys方法返回的是一个数组，所以它有length值

var input= {"A":["B","C"],"B":["D","C","F"],"C":["E"],"D":[],"E":["D"],"F":["E","C"]}
var  zifuchuan = Object.keys(input);// [ 'A', 'B', 'C', 'D', 'E', 'F' ]
var len=zifuchuan.length;//6

json对象的key、value

var  arr = {1:'a',2:'b',3:'c',4:'d',5:'e'};
   console.log(arr.length);  //undefined
   console.log(Object.keys(arr).length); //5
   for(var k in arr){
        console.log(k);
        console.log(arr[k]);
   }