Rails：无法读取 null 的属性“addEventListener”[重复]答案

【问题标题】：Rails: Cannot read property 'addEventListener' of null [duplicate]Rails：无法读取 null 的属性“addEventListener”[重复]
【发布时间】：2018-03-17 15:45:09
【问题描述】：

在让addEventListener 工作时遇到问题。我认为document.querySelector 出了点问题，但不确定为什么它返回 null。

这是我的 index.html：

<% @title="Versatile Contracting Group | Home" %>
<section id="showcase">
  <div class="container">
    <h1>Versatile Contracting Group</h1>
    <p> Lorem minim anim quorum veniam veniam elit velit eram cillum export aute summis</p>
  </div>
</section>
<section id="boxes">
  <div class="container">
    <div class="box">
      <%= image_tag("logo_brush.png", :alt => "stones pic") %>
      <h2>Stone, Vaneer, Concrete and Paver</h2>
      <p>We transform patios, walkways, driveways, walls, columns, subdivision monument signs, and more!</p>
    </div>
    <div class="box">
      <%= image_tag("logo_css.png", :alt => "stones pic") %>
      <h2>Outdoor Firepits and Kitchens</h2>
      <p>Take your backyard to the next level with a kitchen or firepit</p>
    </div>
    <div class="box">
      <%= image_tag("logo_html.png", :alt => "stones pic") %>
      <h2>Grading and Drainage Services</h2>
      <p>We take care of all grading and drainage work, while making your space look incredible</p>
    </div>
  </div>
  <!-- Add picture slideshow -->
</section>
<div class="wrap">
  <div id="arrow-left" class="arrow"></div>
  <div id="slider">
    <div class="slide slide1">
      <div class="slide-content">
      </div>
    </div>
    <div class="slide slide2">
      <div class="slide-content">
        <span></span>
      </div>
    </div>
    <div class="slide slide3">
      <div class="slide-content">
        <span></span>
      </div>
    </div>
  </div>
  <div id="arrow-right" class="arrow"></div>
</div>

这是我的welcome.js：

let sliderImages = document.querySelectorAll(".slide"),
  arrowLeft = document.querySelector("#arrow-left"),
  arrowRight = document.querySelector("#arrow-right"),
  current = 0;

// Clear all images
function reset() {
  for (let i = 0; i < sliderImages.length; i++) {
    sliderImages[i].style.display = "none";
  }
}

// Init slider
function startSlide() {
  reset();
  sliderImages[0].style.display = "block";
}

// Show prev
function slideLeft() {
  reset();
  sliderImages[current - 1].style.display = "block";
  current--;
}

// Show next
function slideRight() {
  reset();
  sliderImages[current + 1].style.display = "block";
  current++;
}

// Left arrow click
arrowLeft.addEventListener("click", function() {
  if (current === 0) {
    current = sliderImages.length;
  }
  slideLeft();
});

// Right arrow click
arrowRight.addEventListener("click", function() {
  if (current === sliderImages.length - 1) {
    current = -1;
  }
  slideRight();
});

startSlide();

【问题讨论】：

标签： javascript ruby-on-rails dom erb

【解决方案1】：

您可能会在页面加载之前包含脚本。将脚本移动到正文底部或使用 DOMContentLoaded

document.addEventListener("DOMContentLoaded", function(event) {
    console.log("DOM fully loaded and parsed");
  });

【讨论】：

将它移到底部有帮助！太聪明了！