判断字符串是不是json字符串

从对象中解析出字符串
var test = {"name":"xiao"};
var obj = JSON.stringify(test);
将字符串解析成对象
var test = '{"name":"xiao"}';
var json = JSON.parse(test);

判断是不是json字符串
var aa = JSON.stringify({"reg_phone":"nao"});
function isJSON(str) {
if (typeof str == 'string') {
try {
var obj=JSON.parse(str);
if(typeof obj == 'object' && obj ){
console.log(3)
return true;
}else{
return false;
}

    } catch(e) {
        console.log('error：'+str+'!!!'+e);
        return false;
    }
}
console.log('It is not a string!')

}
isJSON(aa); //true,则aa是json字符串
isJSON(aa); //It is not a string! ,则aa不是json字符串