event.initEvent(type[, bubbles[, cancelable]])
稳定性: 3 - 旧版：WHATWG 规范认为它已弃用，用户根本不应使用它。
¥Stability: 3 - Legacy: The WHATWG spec considers it deprecated and users shouldn't use it at all.
事件构造函数冗余且无法设置 composed。这在 Node.js 中没有使用，纯粹是为了完整性而提供的。
¥Redundant with event constructors and incapable of setting composed.
This is not used in Node.js and is provided purely for completeness.