Content download synchronization

Question

I have four html-elements, in which at different speeds from the server comes a different amount of content (text and images). How can i show their contents only after all the content has come to all elements?

I want to initially show placeholders, and remove them only when I have all content ready to show for user.

Answer 1

While i find this random image API painfully slow, it is good for a demonstration. You may approach as follows;

var imgPrs = Array.from({length: 4})
                  .map(_ => fetch("https://unsplash.it/300/400/?random").then(res => res.blob()));
Promise.all(imgPrs)
  .then(blob => document.querySelectorAll("#container img")
                        .forEach((img, i) => img.src = (window.URL || window.webkitURL).createObjectURL(blob[i])));

#container {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-evenly;
  align-items: center;
  width: 80vw;
  height: 60vw;
  background-color: #000;
  box-sizing: border-box;
}

.tl {
  width: 45%;
  height: 45%;
  background-color: #ccc;
}

.tr {
  width: 45%;
  height: 45%;
  background-color: #bbb;
}

.bl {
  width: 45%;
  height: 45%;
  background-color: #aaa;
}

.br {
  width: 45%;
  height: 45%;
  background-color: #999;
}

<div id="container">
  <img class="tl">
  <img class="tr">
  <img class="bl">
  <img class="br">
</div>