问如何检查一个JSON响应元素是否是一个数组？

    {
    "timetables":[
        {"id":87,"content":"B","language":"English","code":"en"},                                                
        {"id":87,"content":"a","language":"Castellano","code":"es"}],
    "id":6,
    "address":"C/Maestro José"
    }

for(var i in json) {            
    if(json[i]  is Array) {
    // Iterate the array and do stuff
    } else {
    // Do another thing
    }
}