flip

import {flip} from '@floating-ui/dom';

Usage

computePosition(referenceEl, floatingEl, {
  middleware: [flip()],
});

Options

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

interface FlipOptions extends DetectOverflowOptions {
  mainAxis?: boolean;
  crossAxis?: boolean | 'alignment';
  fallbackAxisSideDirection?: 'none' | 'start' | 'end';
  flipAlignment?: boolean;
  fallbackPlacements?: Array<Placement>;
  fallbackStrategy?: 'bestFit' | 'initialPlacement';
}

mainAxis

default: true

This is the main axis in which overflow is checked to perform a flip. By disabling this, it will ignore overflow.

• y-axis for 'top' and 'bottom' placements
• x-axis for 'left' and 'right' placements

flip({
  mainAxis: false,
});

crossAxis

default: true

This is the cross axis in which overflow is checked to perform a flip, the axis perpendicular to mainAxis. By disabling this, it will ignore overflow.

flip({
  crossAxis: false,
});

fallbackAxisSideDirection

default: 'none'

Whether to allow fallback to the opposite axis if no placements along the preferred placement axis fit, and if so, which side direction along that axis to choose. If necessary, it will fallback to the other direction.

• 'none' signals that no fallback to the opposite axis should take place.
• 'start' represents 'top' or 'left'.
• 'end' represents 'bottom' or 'right'.

For instance, by default, if the initial placement is set to 'right', then the placements to try (in order) are:

['right', 'left']

On a narrow viewport, it’s possible or even likely that neither of these will fit.

By specifying a string other than 'none', you allow placements along the perpendicular axis of the initial placement to be tried. The direction determines which side of placement is tried first:

flip({
  fallbackAxisSideDirection: 'start',
});

The above results in: ['right', 'left', 'top', 'bottom'].

flip({
  fallbackAxisSideDirection: 'end',
});

The above results in: ['right', 'left', 'bottom', 'top'].

As an example, if you’d like a tooltip that has a placement of 'right' to be placed on top on mobile (assuming it doesn’t fit), then you’d use 'start'. For an interactive popover, you likely want to use 'end' so it’s placed on the bottom, closer to the user’s fingers.

In each of the following demos, the placement is 'right'.

flipAlignment

default: true

When an alignment is specified, e.g. 'top-start' instead of just 'top', this will flip to 'top-end' if start doesn’t fit.

flip({
  flipAlignment: false,
});

When using this with the shift() middleware, ensure flip() is placed before shift() in your middleware array. This ensures the flipAlignment logic can act before shift()’s does.

fallbackPlacements

default: [oppositePlacement]

This describes an explicit array of placements to try if the initial placement doesn’t fit on the axes in which overflow is checked.

flip({
  fallbackPlacements: ['right', 'bottom'],
});

In the above example, if placement is set to 'top', then the placements to try (in order) are:

['top', 'right', 'bottom']

fallbackStrategy

default: 'bestFit'

When no placements fit, then you’ll want to decide what happens. 'bestFit' will use the placement which fits best on the checked axes. 'initialPlacement' will use the initial placement specified.

flip({
  fallbackStrategy: 'initialPlacement',
});

…detectOverflowOptions

All of detectOverflow’s options can be passed. For instance:

flip({
  padding: 5, // 0 by default
});

Deriving options from state

You can derive the options from the middleware lifecycle state:

flip((state) => ({
  padding: state.rects.reference.width,
}));

Final placement

The placement returned from the function is always the final one, not necessarily the one you passed in as the “preferred” one.

computePosition(referenceEl, floatingEl, {
  placement: 'bottom',
  middleware: [flip()],
}).then(({placement}) => {
  console.log(placement); // 'top' or 'bottom'
});

Combining with shift()

When using flip() with shift() together, the recommended configuration is as follows:

const middleware = [offset(5)];
const flipMiddleware = flip({
  // Ensure we flip to the perpendicular axis if it doesn't fit
  // on narrow viewports.
  crossAxis: 'alignment',
  fallbackAxisSideDirection: 'end', // or 'start'
});
const shiftMiddleware = shift();
 
// Prioritize flip over shift for edge-aligned placements only.
if (placement.includes('-')) {
  middleware.push(flipMiddleware, shiftMiddleware);
} else {
  middleware.push(shiftMiddleware, flipMiddleware);
}

This results in the most expected positioning when using both middleware regardless of the placement used.

Conflict with autoPlacement()

flip() and autoPlacement() cannot be used together inside the same middleware array; make sure you choose only one of them to use.

The reason is they both try to perform work on the placement but with opposing strategies. Therefore, they will continually try to change the result or work of the other one, leading to a reset loop.

• flip() uses a fallback “no space” strategy. Ensures the preferred placement is kept unless there is no space left.
• autoPlacement() uses a primary “most space” strategy. Always chooses the placement with the most space available.