ReadyState

未连接：尚未建立连接

连接中：正在建⽴连接，还没有完成

连接已打开：连接成功建⽴，可以进⾏通信

关闭中：连接正在进⾏关闭握⼿，即将关闭

已关闭：连接已经关闭或者根本没有建⽴

Returns a representation of an immutable list of all enum entries, in the order they're declared.

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Returns an array containing the constants of this enum type, in the order they're declared.