模态图像不起作用

Question

我需要一些帮助。我正在尝试在我正在设计的网站上使用模态图像，但是当我尝试它时没有任何反应。理想的行为是我想要点击图像，然后会出现模态。下面，我发布了代码。我已经包含了与此功能相关的HTML，CSS和JavaScript部分的代码。任何帮助将不胜感激，欢呼！

// Get the modal
var modal = document.getElementById("picModal");

// Get the image and insert it inside the modal - use its "alt" text as a caption
var img = document.getElementById("proImg");
var modalImg = document.getElementById("img01");
var captionText = document.getElementById("caption");
img.onclick = function() {
  modal.style.display = "block";
  modalImg.src = this.src;
  captionText.innerHTML = this.alt;
}

// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];

// When the user clicks on <span> (x), close the modal
span.onclick = function() {
  modal.style.display = "none";
}

#proImg {
  border-radius: 5px;
  cursor: pointer;
  transition: 0.3s;
}

#proImg:hover {
  opacity: 0.7;
}

.modal {
  display: none;
  /*Hides by default*/
  position: fixed;
  /*Keeps in place*/
  z-index: 1;
  /*Displays over everything*/
  padding-top: 100px;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  /*Enable scroll if needed*/
  background-color: rgb(0, 0, 0);
  background-color: rgba(0, 0, 0, 0.9);
  /*Black w.opacity*/
}

.modal-content {
  margin: auto;
  display: block;
  width: 80%;
  max-width: 600px;
}

#caption {
  margin: auto;
  display: block;
  width: 80%;
  max-width: 600px;
  text-align: center;
  color: #ccc;
  padding: 10px 0;
  height: 150px;
}


/*Animation - Zoom in the Modal*/

.modal-content,
#caption {
  -webkit-animation-name: zoom;
  -webkit-animation-duration: 0.6s;
  animation-name: zoom;
  animation-duration: 0.6s;
}

@-webkit-keyframes zoom {
  from {
    -webkit-transform: scale(0)
  }
  to {
    -webkit-transform: scale(1)
  }
}

@keyframes zoom {
  from {
    transform: scale(0)
  }
  to {
    transform: scale(1)
  }
}


/* The Modal Close Button*/

.close {
  position: absolute;
  top: 15px;
  right: 35px;
  color: #f1f1f1;
  font-size: 40px;
  font-weight: bold;
  transition: 0.3s;
}

.close:hover,
.close:focus {
  color: #bbb;
  text-decoration: none;
  cursor: pointer;
}


/* 100% Image Width on Smaller Screens */

@media only screen and (max-width: 600px) {
  .modal-content {
    width: 100%;
  }
}

<img src="https://placeimg.com/100/100/any" id="proImg" class="product-image" alt="This is an image">
<!-- Modal Div -->
<div id="picModal" class="modal">
  <!-- Close Button -->
  <span class="close">X</span>
  <!-- Modal Image -->
  <img class="modal-content" id="img01">
  <!-- Modal Caption -->
  <div id="caption"></div>
</div>