How do I check if a particular key exists in a JavaScript object or array? 如何检查JavaScript对象或数组中是否存在特定键? 数组
If a key doesn't exist, and I try to access it, will it return false? 若是密钥不存在,而我尝试访问它,它将返回false吗? Or throw an error? 仍是抛出错误? spa