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HTML

              
                <main>
  <section id="example01">
    <h1>例外の伝播をわざと catch しない例</h1>
    <p><button>押して開始</button></p>
    <div class="console" />
  </section>
  <section id="example02">
    <h1>例外の伝播を catch でハンドリングする例</h1>
    <p><button>押して開始</button></p>
    <div class="console" />
  </section>
</main>
              
            
!

CSS

              
                *,
*::berore,
*::after {
  box-sizing: border-box;
}

h1 {
  margin-top: 0;
}

main {
  display: grid;
  align-items: flex-start;
  grid-template-columns: repeat(auto-fit, minmax(49%, 1fr));
  gap: 1rem;
  justify-content: center;
  line-height: 1.4;
}

section {
  border: 1px solid #444;
  border-radius: 2rem;
  padding: 2rem;
}

              
            
!

JS

              
                const failExample = document.querySelector("#example01");
const failButton = failExample.querySelector("button");
failButton.addEventListener("click", failSleep);
const failConsole = document.querySelector("#example01 .console");

/**
 * 例外の伝播を無視するコード例
 */
async function failSleep(e) {
  const consoleNode = clearConsole(failConsole);
  createNode(consoleNode, "article", "イベントハンドラ関数を実行");

  await sleep(1000);
  await otherFn(consoleNode);
}

const catchExample = document.querySelector("#example02");
const catchButton = catchExample.querySelector("button");
catchButton.addEventListener("click", catchSleep);
const catchConsole = document.querySelector("#example02 .console");

/**
 * 例外の伝播をハンドリングするコード例
 */
async function catchSleep(e) {
  const consoleNode = clearConsole(catchConsole);
  createNode(consoleNode, "article", "イベントハンドラ関数を実行");
  await sleep(1000);

  // ここでハンドリング!
  try {
    await otherFn(consoleNode);
  } catch (err) {
    // ハンドリング処理をここに記述
    createNode(catchConsole, "p", "例外を受け取りました!");
  }
}

/**
 * 例外の伝播を示すために、経由させる関数
 */
async function otherFn(catchConsole) {
  createNode(catchConsole, "article", "上記からさらに呼び出された関数を実行");
  await sleep(1000);
  return raiseExeption(catchConsole);
}

/**
 * 例外を発行する関数
 */
function raiseExeption(catchConsole) {
  createNode(catchConsole, "article", "例外を発行する関数を実行");

  const a = "beact";
  a.b.c = 1;

  return a;
}

/**
 * テストコード用:画面のコンソール部をクリア
 */
function clearConsole(consoleNode) {
  while (consoleNode.lastChild) {
    consoleNode.removeChild(consoleNode.lastChild);

    // DOMツリーから取り除いたら、GCの対象にする
    consoleNode.lastChild = null;
  }

  return consoleNode;
}

/**
 * テストコード用:DOMノード生成&アペンド関数
 */
function createNode(targetNode, tagName, textContent) {
  const node = document.createElement(tagName);
  node.textContent = textContent;
  targetNode.appendChild(node);

  return targetNode;
}

/**
 * テストコード用:非同期処理用のダミー関数
 */
function sleep(ms = 1000) {
  return new Promise((res) => {
    setTimeout(() => res(), ms);
  });
}

              
            
!
999px

Console