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HTML

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CSS

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JavaScript

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HTML 

              
                <h1>Measuring Performance</h1>
<p>
Click "Start Task" to simulate an asynchronous task and capture performance marks and a measure.
</p>

<p>
Click "Reset" to clear the performance timeline.
</p>

<button id="button">Start Task</button>
<button id="reset">Reset</button>

<ul>
  
</ul>
!

CSS 

              
                * {
  font-family: Arial, sans-serif;
}

pre {
  font-family: Courier New, monospace;
  background: #333;
  color: white;
}

details {
  padding: 8px;
}

@keyframes appear {
  from {
    opacity: 0;
    transform: scale(0.8);
  }
  
  to {
    opacity: 1;
    transform: scale(1);
  }
}

button {
  background: #4338ca;
  color: white;
  padding: 8px 16px;
  font-size: 1.2em;
  border: 1px solid transparent;
  border-radius: 5px;
  cursor: pointer;
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.5;
}

ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}

.mark {
  border: 1px solid gray;
  margin-top: 8px;
  margin-right: 8px;
  border-radius: 3px;
  background: #e0f2fe;
  animation: appear 500ms;
}

.mark h2 {
  margin: 0;
  font-size: 1.25rem;
  background: #1e40af;
  color: white;
  padding: 8px;
}

.mark dl {
  font-size: 1.2rem;
  padding: 8px;
  display: grid;
  grid-template-columns: auto 1fr;
  margin: 0;
}

.mark dt {
  font-weight: bold;
}

.mark dd {
  font-family: Courier, monospace;
}

.measure {
  background: #dcfce7;
}

.measure h2 {
  background: #166534;
}
!

JS 

              
                const button = document.querySelector('#button');
const reset = document.querySelector('#reset');
const list = document.querySelector('ul');

let taskId = 1;

function showMark(mark) {
  const el = document.createElement('li');
  el.className = 'mark';

  el.innerHTML = `
    <h2>Performance Mark</h2>
    <dl>
      <dt>Name</dt>
      <dd>${mark.name}</dd>
      <dt>Start Time</dt>
      <dd>${mark.startTime}</dd>
    </dl>
    <details>
      <summary>Full entry details</summary>
      <pre>${JSON.stringify(mark, null, 2)}</pre>
    </details>
  `;
  
  list.insertBefore(el, list.firstElementChild);
}

function showMeasure(measure, startMark, endMark) {
  const el = document.createElement('li');
  el.className = 'measure mark';

  el.innerHTML = `
    <h2>Performance Measure</h2>
    <dl>
      <dt>Name</dt>
      <dd>${measure.name}</dd>
      <dt>Start Mark</dt>
      <dd>${startMark}</dd>
      <dt>End Mark</dt>
      <dd>${endMark}</dd>
      <dt>Duration</dt>
      <dd>${measure.duration}</dd>
    </dl>
    <details>
      <summary>Full entry details</summary>
      <pre>${JSON.stringify(measure, null, 2)}</pre>
    </details>
  `;
  
  list.insertBefore(el, list.firstElementChild);
}

reset.addEventListener('click', () => {
  performance.clearMarks();
  performance.clearMeasures();
  
  list.replaceChildren();
});

button.addEventListener('click', () => {
  button.disabled = true;
  const startMark = performance.mark(`task-${taskId}-start`);
  showMark(startMark);
  
  const delay = Math.random() * 4000;
  setTimeout(() => {
    const endMark = performance.mark(`task-${taskId}-end`);
    showMark(endMark);
    const measure = performance.measure(`task-${taskId}`, `task-${taskId}-start`, `task-${taskId}-end`);
    setTimeout(() => showMeasure(measure, `task-${taskId}-start`, `task-${taskId}-end`), 200);
    taskId++;
    button.disabled = false;
  }, delay);
});
!
999px

Console