check.js

function createNgElement(reason) {
  const ng = document.createElement("span")
  ng.style.position = "relative"
  ng.style.top = "0"
  ng.style.left = "0"
  ng.style.zIndex = "9999"
  ng.style.width = "20px"
  ng.style.height = "20px"
  ng.style.padding = "0 10px"
  ng.style.backgroundColor = "#d42d2d"
  ng.style.color = "#fff"
  ng.style.fontSize = "12px"
  ng.style.opacity = "0.7"
  ng.className = "link-checker-ng"
  ng.innerText = reason
  return ng;
}

function linkCheck(list) {
  if(list.length === 0) return;
  const [a, ...xs] = list
  const href = a.getAttribute("href")
  
  if(href === "") {
    const ng = createNgElement("href=''")
    a.appendChild(ng)
    linkCheck(xs)
    return;
  }
  if(href === "#") {
    const ng = createNgElement("href='#'")
    a.appendChild(ng)
    linkCheck(xs)
    return;
  }
  
  fetch(href, {mode: 'no-cors'}).then((res) => {
    linkCheck(xs)
    return res
  }).then((res) => {
    if(res.body === null) {
      const ng = createNgElement("unchecked")
      a.appendChild(ng)
      return;
    }
    if(!res.ok) {
      const ng = createNgElement("ng")
      a.appendChild(ng)
      return
    }
  })
  
}

linkCheck(Array.from(document.querySelectorAll("a")))