import inline from '../../assets/virtual-elements.inline.jpg';

# Virtual Elements

A floating element can be positioned relative to a virtual
reference element instead of a real one.

<CircleImage name="virtual-elements" inline={inline} />

This enables features such as positioning context menus,
following the cursor, range selections, etc.

## Usage

The most basic virtual element is a plain object that has a
`getBoundingClientRect{:.function}` method, which mimics a real
element's one:

```js
// A virtual element that is 20 x 20 px starting from (0, 0)
const virtualEl = {
  getBoundingClientRect() {
    return {
      x: 0,
      y: 0,
      top: 0,
      left: 0,
      bottom: 20,
      right: 20,
      width: 20,
      height: 20,
    };
  },
};

computePosition(virtualEl, floatingEl);
```

A point reference, such as a mouse event, is one such use case:

```js
function onClick({clientX, clientY}) {
  const virtualEl = {
    getBoundingClientRect() {
      return {
        width: 0,
        height: 0,
        x: clientX,
        y: clientY,
        top: clientY,
        left: clientX,
        right: clientX,
        bottom: clientY,
      };
    },
  };

  computePosition(virtualEl, floatingEl).then(({x, y}) => {
    // Position the floating element relative to the click
  });
}

document.addEventListener('click', onClick);
```

## contextElement

This property is useful if your
`getBoundingClientRect{:.function}` method is derived from a real
element, to ensure clipping and position update detection works
as expected.

```js
const virtualEl = {
  getBoundingClientRect() {
    return {
      // ...
    };
  },
  contextElement: document.querySelector('#context'),
};
```

## getClientRects

This property is useful when using range selections and the
`inline(){:js}` middleware.

```js
const virtualEl = {
  getBoundingClientRect: () => range.getBoundingClientRect(),
  getClientRects: () => range.getClientRects(),
};
```