function isJSON(str) {

    if (typeof str == 'string') {

        try {

            var obj=JSON.parse(str);

            if(typeof obj == 'object' && obj ){

                return true;

            }else{

                return false;

            }

        } catch(e) {

            console.log('error：'+str+'!!!'+e);

            return false;

        }

    }

    console.log('It is not a string!')

}