buggy_mutation_observer_workaround.ts

(async () => {
  if (await mutionObserverIsBuggy()) {
    patchInnerHTML()
  }
})()

function mutionObserverIsBuggy(): Promise<boolean> {
  return new Promise(resolve => {
    const element = document.createElement("div")
    element.innerHTML = "<a><em></em></a>"

    const observer = new MutationObserver(mutations => {
      for (const mutation of mutations) {
        if (mutation.type == "childList") {
          const node = mutation.removedNodes[0]
          const isBuggy = node.childNodes.length == 0
          observer.disconnect()
          return resolve(isBuggy)
        }
      }
    })
    observer.observe(element, { childList: true, subtree: true })
    element.innerHTML = ""
  })
}

function patchInnerHTML() {
  const { prototype } = HTMLElement
  const descriptor = Object.getOwnPropertyDescriptor(prototype, "innerHTML")

  if (descriptor) {
    Object.defineProperty(prototype, "innerHTML", {
      get() {
        if (typeof descriptor.get == "function") {
          return descriptor.get.call(this)
        }
      },
      set(value) {
        while (this.lastChild) {
          this.removeChild(this.lastChild)
        }
        if (typeof descriptor.set == "function") {
          return descriptor.set.call(this, value)
        }
      }
    })
  }
}