Introduction to Anchor Position API

What is the Anchor Positioning API?

The Anchor Positioning API allows developers to dynamically position elements relative to an “anchor” element in the viewport. Unlike traditional CSS positioning (absolute, fixed, sticky), it automatically aligns elements, handles collisions, and adjusts when the anchor or viewport changes.

Think of it like attaching a tooltip, dropdown, or popup to a button—no manual calculations needed.

How It Works

Anchor Element: The reference element (e.g., button).
Positioned Element: The floating element (e.g., tooltip or popup).
Placement Options: top, bottom, left, right.
Collision Detection: Keeps elements inside the viewport automatically.

Why Use Anchor Position API?

Dynamic Alignment: Automatically positions tooltips, popups, menus, or modals relative to their anchor.
Responsive Behavior: Adjusts when the anchor moves, the viewport changes, or elements resize.
Collision Detection: Prevents elements from going off-screen by repositioning automatically.
Simplifies Layouts: Reduces complex CSS or JavaScript calculations.
Modern Web Standards: Works seamlessly with modern browsers, CSS, and JavaScript.

Core Concepts

Anchor Element: The reference element (e.g., button, link, or card).
Positioned Element: The floating element (e.g., tooltip, popup, dropdown).
Viewport Reference: Ensures the element stays visible and aligned in the viewport.
Collision Handling: Automatically repositions elements if they might overflow.

Basic Syntax

const anchor = document.querySelector('#button');
const popup = document.querySelector('#popup');

popup.showPopover(anchor, {
  placement: 'bottom',   // top, bottom, left, right
  offset: 8,             // distance from anchor
  collision: 'flip',     // flips automatically if element overflows
});

Simple Example

Here’s a basic example using the Anchor Positioning API to show a tooltip near a button:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Anchor Position API Example</title>
  <style>
    body {
      font-family: Arial, sans-serif;
      padding: 50px;
    }

    button {
      padding: 10px 20px;
      font-size: 16px;
      cursor: pointer;
    }

    #tooltip {
      position: absolute;
      padding: 10px 15px;
      background-color: #3498db;
      color: white;
      border-radius: 5px;
      display: none;
      white-space: nowrap;
    }
  </style>
</head>
<body>

  <button id="myButton">Hover Me!</button>
  <div id="tooltip">This is a tooltip using Anchor Position API.</div>

  <script>
    const button = document.getElementById('myButton');
    const tooltip = document.getElementById('tooltip');

    button.addEventListener('mouseenter', () => {
      tooltip.style.display = 'block';

      // Anchor Position API using getBoundingClientRect
      const rect = button.getBoundingClientRect();
      tooltip.style.top = `${rect.bottom + window.scrollY + 8}px`; // 8px offset
      tooltip.style.left = `${rect.left + window.scrollX}px`;
    });

    button.addEventListener('mouseleave', () => {
      tooltip.style.display = 'none';
    });
  </script>

</body>
</html>