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？)
If a key doesn't exist, and I try to access it, will it return false?
(如果密钥不存在，而我尝试访问它，它将返回false吗？)
Or throw an error?(还是抛出错误？)
ask by Adam Ernst translate from so
