将按键功能添加到JavaScript

Question

感谢所有为我直接或间接提出的问题提供答案的人。我已经看到了类似的问题，但一直没有答案。

我已将W3的Lightbox Modal添加到我的网站。在Lightbox库中循环可以使用光标选择指定的close，previous和next按钮。但是，我想添加以下按键功能：escape key = close，left arrow = prev，right arrow = next。在研究时我已经看到了启用这些功能的JavaScript KeyCodes（37,39等），但我很难将它们粘贴到实际的代码中。热烈欢迎任何帮助。谢谢。

     function openModal() {
     document.getElementById('myModal').style.display = "block";
     }
     function closeModal() {
     document.getElementById('myModal').style.display = "none";
     }
     var slideIndex = 1;
     showSlides(slideIndex);

     function plusSlides(n) {
       showSlides(slideIndex += n);
     }
     function currentSlide(n) {
       showSlides(slideIndex = n);
     }
     function showSlides(n) {
       var i;
       var slides = document.getElementsByClassName("mySlides");
       var dots = document.getElementsByClassName("demo");
       var captionText = document.getElementById("caption");
       if (n > slides.length) {slideIndex = 1}
       if (n < 1) {slideIndex = slides.length}
       for (i = 0; i < slides.length; i++) {
         slides[i].style.display = "none";
       }
       for (i = 0; i < dots.length; i++) {
         dots[i].className = dots[i].className.replace(" active", "");
       }
       slides[slideIndex-1].style.display = "block";
       dots[slideIndex-1].className += " active";
       captionText.innerHTML = dots[slideIndex-1].alt;
       }

     <div id="myModal" class="modal" style="display: none;">
             <span class="close cursor" onclick="closeModal()">×</span>
               <div id="center-slides">
                  <div class="modal-content">
                  <div class="mySlides" style="display: none;">
                <div class="numbertext">1 / 14</div>
                <img src="OptimizedWebGraphics/People/Portfolio_People-                  
       6.jpg" alt="A sign written in chalk following a couple's love story"                   
    class="landscape-pic"></div>
            <div class="mySlides" style="display: none;">
                <div class="numbertext">2 / 4</div>
        <img src="OptimizedWebGraphics/People/Portfolio_People-4.jpg" alt="a newly married couple embrace" class="portrait-pic"></div>
            <div class="mySlides" style="display: none;">
                <div class="numbertext">3 / 4</div>
                <img src="OptimizedWebGraphics/People/FifthHouse_WatermarkedPhotos-65.jpg" alt="a man and woman clink wine glasses" class="landscape-pic"></div>
            <div class="mySlides" style="display: none;">
                <div class="numbertext">4 / 4</div>
                <img src="OptimizedWebGraphics/People/Portfolio_People-8.jpg" alt="women smiling" class="landscape-pic"></div>
            <div class="mySlides" style="display: none;">
    <a class="prev" onclick="plusSlides(-1)">❮</a>
    <a class="next" onclick="plusSlides(1)">❯</a>
          </div></div>
  <div class="caption-container">
        <p id="caption"></p></div>
      </div>

感谢您的帮助