Beispiele für JavaScript-Beobachter

1. ResizeObserver
2. IntersectionObserver
3. MutationObserver

Größe des Beobachters ändern

Geplanter Termin

Theorie

Unterstützung

Beispiel

<div id="box" class="box">
  <h1 id="title" class="title">Some Awesome Title</h1>
  <p id="text" class="text">Some Main Text</p>
  <span id="info" class="info">Some Secondary Info</span>
</div>

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
.box,
.title,
.text,
.info {
  transition: 0.3s;
}
.box {
  background: #ddd;
  color: #222;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  align-items: center;
}
.title,
.info {
  margin: 1rem;
}
.title {
  font-size: 2rem;
}
.text {
  font-size: 1.25rem;
}

//     
const changeStyles = (elements, properties, values) =>
  elements.forEach((element, index) => {
    element.style[properties[index]] = values[index];
  });

//   ResizeObserver
const observer = new ResizeObserver((entries) => {
  //     (  )
  for (const entry of entries) {
    //    
    const width = entry.contentRect.width;

    //  
    //      768px
    //   
    if (width < 768) {
      changeStyles(
        [box, title, text, info],
        ["filter", "fontSize", "fontSize", "opacity"],
        ["invert(100%)", "1.5rem", "1rem", "0"]
      );
    } else {
      //      768px
      //  
      changeStyles(
        [box, title, text, info],
        ["filter", "fontSize", "fontSize", "opacity"],
        ["invert(0%)", "2rem", "1.25rem", "1"]
      );
    }
  }
});

//       "box"
observer.observe(box);

IntersectionObserver

Geplanter Termin

Theorie

Unterstützung

Beispiel

<main id="main">
  <section id="1" class="section">
    <h3 class="title">First Section Title</h3>
    <p class="text">
      Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ipsam nostrum ex delectus distinctio reprehenderit facere vitae beatae ab dolores, aliquam maiores officia mollitia unde et! Quaerat odit in minus dolor corrupti nemo nam beatae. Ex consequatur rem laborum necessitatibus omnis, soluta fuga maiores repellendus eveniet? Blanditiis quae officiis maiores vitae nobis in voluptate, dicta voluptas rerum. Et laudantium consequuntur vitae tenetur doloremque accusantium tempora quos magni repudiandae voluptatem perferendis velit reprehenderit laborum libero soluta quis id, quidem assumenda nihil obcaecati expedita, aliquam suscipit nesciunt facere. Voluptate rem perferendis ab iste? Maxime, earum quos! Modi, aut quis nihil quidem accusamus vero sunt debitis architecto soluta repellendus fugit suscipit aspernatur labore a est sit dolores in necessitatibus ea tenetur corporis. Exercitationem mollitia impedit qui nemo voluptate numquam perspiciatis repellendus repellat a odio fugit dolor ducimus labore ex veritatis pariatur aliquam enim distinctio libero doloremque saepe quaerat consectetur, ut sapiente. Laboriosam dignissimos iure praesentium modi ab perferendis at molestias maiores suscipit, expedita aut aperiam nam voluptates similique optio minus quam! Voluptas ullam sunt, a officiis accusamus adipisci sed saepe voluptatem minima maxime est assumenda cum quibusdam voluptates provident in quasi vitae. Corrupti voluptatibus laborum ipsum quia, cupiditate adipisci assumenda dolores sunt distinctio, recusandae nesciunt aliquid, explicabo ullam eligendi perspiciatis rerum architecto? Cumque numquam blanditiis, magnam delectus velit laudantium aliquid quibusdam excepturi vero nihil necessitatibus, sed officiis, molestias hic autem modi consequuntur iusto sapiente dolore. Voluptates tenetur provident eius distinctio iure rerum minima eum eaque. Ea autem, deleniti atque magnam eius modi dicta assumenda tempore ducimus molestias. Aperiam enim tenetur, hic blanditiis velit quod odio deserunt sequi quisquam dignissimos animi amet magnam excepturi dicta quidem error quis officia natus. Temporibus nobis dolores veritatis eius illo quas perspiciatis reiciendis dolorum optio, commodi, animi quos at! Amet praesentium totam ab error esse optio quo, quis iusto!
    </p>
  </section>
  <section id="2" class="section">
    <h3 class="title">Second Section Title</h3>
    <p class="text">
      ...
    </p>
  </section>
  <section id="3" class="section">
    <h3 class="title">Third Section Title</h3>
    <p class="text">
      ...
    </p>
  </section>
</main>

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  background: #eee;
  color: #222;
  text-align: center;
}
main {
  max-width: 768px;
  margin: auto;
}
.section {
  padding: 1rem;
}
.title {
  font-size: 1.5rem;
  margin: 1rem;
}
.text {
  font-size: 1.25rem;
}

//    ,   
const findLastSection = () => {
  //      
  //   -   
  const number = localStorage.getItem("numberOfSection") || 1;

  //   
  const section = document.getElementById(number);

  //        (  )
  const position = Math.round(section.offsetTop);

  //      
  scrollTo({
    top: position,
    // 
    behavior: "smooth",
  });
};

findLastSection();

//      
const createObserver = () => {
  //   IntersectionObserver
  const observer = new IntersectionObserver(
    (entries) => {
      entries.forEach((entry) => {
        //       
        if (entry.isIntersecting) {
          //      
          localStorage.setItem("numberOfSection", entry.target.id);
        }
      });
    },
    {
      //       
      // 10%
      threshold: 0.1,
    }
  );

  //   
  const sections = main.querySelectorAll("section");
  //    
  sections.forEach((section) => observer.observe(section));
};

createObserver();

MutationObserver

Geplanter Termin

Theorie

Unterstützung

Beispiel

<div id="box" class="box"></div>

@import url("https://fonts.googleapis.com/css2?family=Stylish&display=swap");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: stylish;
  font-size: 1rem;
  color: #222;
}

.box {
  max-width: 512px;
  margin: auto;
  text-align: center;
}

.counter {
  font-size: 2.25rem;
  margin: 0.75rem;
}

.form {
  display: flex;
  margin-bottom: 0.25rem;
}

.input {
  flex-grow: 1;
  border: none;
  border-radius: 4px;
  box-shadow: 0 0 1px inset #222;
  text-align: center;
  font-size: 1.15rem;
  margin: 0.5rem 0.25rem;
}

.input:focus {
  outline-color: #5bc0de;
}

.btn {
  border: none;
  outline: none;
  background: #337ab7;
  padding: 0.5rem 1rem;
  border-radius: 4px;
  box-shadow: 0 1px 1px rgba(0, 0, 0, 0.5);
  color: #eee;
  margin: 0.5rem 0.25rem;
  cursor: pointer;
  user-select: none;
  width: 92px;
  text-shadow: 0 0 1px rgba(0, 0, 0, 0.5);
}

.btn:active {
  box-shadow: 0 0 1px rgba(0, 0, 0, 0.5) inset;
}

.btn.danger {
  background: #d9534f;
}

.list {
  list-style: none;
}

.item {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
}

.item + .item {
  border-top: 1px dashed rgba(0, 0, 0, 0.5);
}

.text {
  flex: 1;
  font-size: 1.15rem;
  margin: 0.5rem;
  padding: 0.5rem;
  background: #eee;
  border-radius: 4px;
}

// 
const todos = [
  {
    id: "1",
    text: "Learn HTML",
  },
  {
    id: "2",
    text: "Learn CSS",
  },
  {
    id: "3",
    text: "Learn JavaScript",
  },
  {
    id: "4",
    text: "Stay alive",
  },
];

//   
const Item = (todo) => `
<li
  class="item"
  id="${todo.id}"
>
  <span class="text"}">
    ${todo.text}
  </span>
  <button
    class="btn danger"
    data-type="delete"
  >
    Delete
  </button>
</li>
`;

//  
const Template = `
<form id="form" class="form">
    <input
      type="text"
      class="input"
      id="input"
    >
    <button
      class="btn"
      data-type="add"
    >
      Add
    </button>
</form>
<ul id="list" class="list">
    ${todos.reduce(
      (html, todo) =>
        (html += `
          ${Item(todo)}
        `),
      ""
    )}
</ul>
`;

//    IIFE
(() => {
  //       "box"
  box.innerHTML = `
  <h1 id="counter" class="counter">
    ${todos.length} todo(s) left
  </h1>
  ${Template}
`;

  //      
  input.focus();

  //   MutationObserver
  const observer = new MutationObserver(() => {
    //     
    const count = todos.length;

    //    ,   ,   ,    
    counter.textContent = `
    ${count > 0 ? `${count} todo(s) left` : "There are no todos"}
  `;
  });

  //        
  observer.observe(list, {
    childList: true,
  });

  //      
  const addTodo = () => {
    if (!input.value.trim()) return;

    const todo = {
      id: Date.now().toString().slice(-4),
      text: input.value,
    };

    list.insertAdjacentHTML("beforeend", Item(todo));

    todos.push(todo);

    input.value = "";
    input.focus();
  };

  //     
  const deleteTodo = (item) => {
    const index = todos.findIndex((todo) => todo.id === item.id);

    item.remove();

    todos.splice(index, 1);
  };

  //     
  form.onsubmit = (e) => e.preventDefault();

  //   
  box.addEventListener("click", (e) => {
    if (e.target.tagName !== "BUTTON") return;

    //      
    const { type } = e.target.dataset;
    const item = e.target.parentElement;

    //          
    switch (type) {
      case "add":
        addTodo();
        break;
      default:
        deleteTodo(item);
        break;
    }
  });
})();