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offset

A placement modifier that translates the floating element along the specified axes.

0px

10px

This enables you to not only add distance between the reference and floating elements, but also create a wide range of custom placements not provided by the library.

Usage

import {computePosition, offset} from '@floating-ui/dom';
 
computePosition(referenceEl, floatingEl, {
  middleware: [offset(10)],
});
import {computePosition, offset} from '@floating-ui/dom';
 
computePosition(referenceEl, floatingEl, {
  middleware: [offset(10)],
});

The value(s) passed are logical, meaning their effect on the physical result is dependent on the placement, writing direction (e.g. RTL), or alignment.

Order

offset()offset() should generally be placed at the beginning of your middleware array.

Options

These are the options you can pass to offset()offset().

interface AxesOffsets {
  mainAxis?: number;
  crossAxis?: number;
  alignmentAxis?: number | null;
}
 
type Options =
  | number
  | AxesOffsets
  | ((
      middlewareArguments: MiddlewareArguments
    ) => number | AxesOffsets);
interface AxesOffsets {
  mainAxis?: number;
  crossAxis?: number;
  alignmentAxis?: number | null;
}
 
type Options =
  | number
  | AxesOffsets
  | ((
      middlewareArguments: MiddlewareArguments
    ) => number | AxesOffsets);

A number represents the distance (gutter or margin) between the floating element and the reference element. This is shorthand for mainAxismainAxis.

offset(10);
offset(10);

An object can also be passed, which enables you to individually configure each axis.

mainAxis

default: 00

Represents the distance (gutter or margin) between the floating element and the reference element.

offset({
  mainAxis: 10,
});
offset({
  mainAxis: 10,
});

Here’s how it looks on the four sides:

top

bottom

left

right

crossAxis

default: 00

Represents the skidding between the floating element and the reference element.

offset({
  crossAxis: 20,
});
offset({
  crossAxis: 20,
});

Here’s how it looks on the four sides:

top

bottom

left

right

alignmentAxis

default: nullnull

Works on the same axis as crossAxiscrossAxis but applies only to aligned placements and works logically. The offset is inverted for -end-end alignments.

This will override the crossAxiscrossAxis offset when set to a number.

offset({
  alignmentAxis: 20,
});
offset({
  alignmentAxis: 20,
});

Here’s how it differentiates from crossAxiscrossAxis:

top-start
(crossAxis)

top-end
(crossAxis)

top-start
(alignmentAxis)

top-end
(alignmentAxis)

Creating custom placements

While you can only choose 12 different placements as part of the core library, you can use the offset()offset() middleware to create any placement you want.

For example, although the library doesn’t provide a placement for centering on both axes, offset enables this via the function option by allowing you to read the rects:

computePosition(referenceEl, floatingEl, {
  middleware: [
    // Assumes placement is 'bottom' (the default)
    offset(({rects}) => {
      return (
        -rects.reference.height / 2 - rects.floating.height / 2
      );
    }),
  ],
});
computePosition(referenceEl, floatingEl, {
  middleware: [
    // Assumes placement is 'bottom' (the default)
    offset(({rects}) => {
      return (
        -rects.reference.height / 2 - rects.floating.height / 2
      );
    }),
  ],
});

10px

In this case, the function option starts from the default bottom placement, then using that starting point, returns an offset to center the floating element on both axes.

A diagonal placement is also possible:

computePosition(referenceEl, floatingEl, {
  placement: 'top-start',
  middleware: [
    offset(({rects}) => ({
      alignmentAxis: -rects.floating.width,
    })),
  ],
});
computePosition(referenceEl, floatingEl, {
  placement: 'top-start',
  middleware: [
    offset(({rects}) => ({
      alignmentAxis: -rects.floating.width,
    })),
  ],
});

This time, 'top-start''top-start' was used as the starting point.

So, it’s straightforward to allow this:

computePosition(referenceEl, floatingEl, {
  placement: 'center',
});
computePosition(referenceEl, floatingEl, {
  placement: 'center',
});

With a wrapper, like this:

import {computePosition as base, offset} from '@floating-ui/dom';
 
const centerOffset = offset(({rects}) => {
  return -rects.reference.height / 2 - rects.floating.height / 2;
});
 
export function computePosition(
  referenceEl,
  floatingEl,
  options
) {
  const isCentered = options.placement === 'center';
  const placement = isCentered ? 'bottom' : options.placement;
  const middleware = [
    isCentered && centerOffset,
    ...(options.middleware || []),
  ];
 
  return base(referenceEl, floatingEl, {
    ...options,
    placement,
    middleware,
  });
}
import {computePosition as base, offset} from '@floating-ui/dom';
 
const centerOffset = offset(({rects}) => {
  return -rects.reference.height / 2 - rects.floating.height / 2;
});
 
export function computePosition(
  referenceEl,
  floatingEl,
  options
) {
  const isCentered = options.placement === 'center';
  const placement = isCentered ? 'bottom' : options.placement;
  const middleware = [
    isCentered && centerOffset,
    ...(options.middleware || []),
  ];
 
  return base(referenceEl, floatingEl, {
    ...options,
    placement,
    middleware,
  });
}
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