@popperjs/core

What is @popperjs/core?

The @popperjs/core package is a powerful positioning engine that allows developers to position elements on a webpage in relation to a reference element. This is particularly useful for creating tooltips, popovers, dropdowns, and more, ensuring they are positioned correctly regardless of viewport size or element positioning.

What are @popperjs/core's main functionalities?

Creating a Tooltip

This code sample demonstrates how to create a simple tooltip positioned to the right of a button. It uses the `createPopper` function from @popperjs/core to dynamically position the tooltip element in relation to the button element.

import { createPopper } from '@popperjs/core';

const tooltip = document.querySelector('#tooltip');
const button = document.querySelector('#button');

createPopper(button, tooltip, {
  placement: 'right',
});

Modifying Popper Behavior with Modifiers

This example shows how to use modifiers to adjust the behavior of a Popper instance. Here, the 'offset' modifier is used to add some space between the reference element and the popper element, specifically 8 pixels along the y-axis.

import { createPopper } from '@popperjs/core';

const popperInstance = createPopper(referenceElement, popperElement, {
  modifiers: [
    {
      name: 'offset',
      options: {
        offset: [0, 8],
      },
    },
  ],
});

Other packages similar to @popperjs/core

tippy.js

Tippy.js is a highly customizable tooltip and popover library that wraps around Popper.js. It offers a simpler API for common tooltip and popover scenarios, making it easier to use out of the box compared to @popperjs/core, which offers more low-level control.

floating-ui

Floating UI is a low-level library for creating floating elements, tooltips, dropdowns, and more, similar to @popperjs/core. It provides a core set of utilities for positioning and updating the UI elements, with a focus on extensibility and customization.

README

Positioning tooltips is difficult. Popper is here to help!

Given an element, such as a button, and a tooltip element describing it, Popper will automatically put the tooltip in the right place near the button.

But Popper is not just about tooltips. It will position any UI element that "pops out" from the flow of your document. The most common example is a tooltip, but it also includes popovers, drop-downs, and more. All of these can be generically described as a "popper element".

Why Popper?

Naive tooltip implementations generally don't consider the following:

• Preventing overflow when the tooltip is near a boundary (e.g. window), it will get cut off;
• Flipping to keep the tooltip visible in the viewport for the user;
• Keeping the tooltip with the reference element when inside any number of scrolling containers;
• Keeping the tooltip in its original DOM context

Popper solves all of these key problems in an elegant, performant manner. It is a ~3 kB library that aims to provide a reliable and extensible positioning engine you can use to ensure all your popper elements are positioned in the right place.

Why waste your time writing your own logic every time you are programming a tooltip? There are many edge cases that are easy to forget to consider, which is why we've done the hard work for you.

Since we write UIs using powerful abstraction libraries such as React or Angular nowadays, you'll also be glad to know Popper can fully integrate with them and be a good citizen together with your other components. Check out react-popper for the official Popper wrapper for React.

Installation

1. Package Manager

# With npm
npm i @popperjs/core@alpha

# With Yarn
yarn add @popperjs/core@alpha

2. CDN

<script src="https://unpkg.com/@popperjs/core@alpha"></script>

3. Direct Download?

Managing dependencies by "directly downloading" them and placing them into your source code is not recommended for a variety of reasons, including missing out on feat/fix updates easily. Please, use a versioning management system like a CDN or npm/Yarn.

Usage

The most straightforward way to get started is to import Popper from the unpkg CDN, which includes all of its features. You can call the Popper.createPopper constructor to create new popper instances.

Here is a complete example:

<!DOCTYPE html>
<title>Popper example</title>

<style>
  #tooltip {
    background-color: rebeccapurple;
    padding: 20px;
    width: 200px;
  }
</style>

<button type="button" id="button">I'm a button</button>
<div id="tooltip">I'm a tooltip</div>

<script src="https://unpkg.com/@popperjs/core@alpha"></script>
<script>
  const button = document.querySelector('#button');
  const tooltip = document.querySelector('#tooltip');

  // Pass the button, the tooltip, and some options, and Popper will do the
  // magic positioning for you:
  Popper.createPopper(button, tooltip, {
    placement: 'right',
  });
</script>

Module bundlers

You can import the createPopper constructor from the fully-featured file:

import { createPopper } from '@popperjs/core';

const button = document.querySelector('#button');
const tooltip = document.querySelector('#tooltip');

// Pass the button, the tooltip, and some options, and Popper will do the
// magic positioning for you:
createPopper(button, tooltip, {
  placement: 'right',
});

All the modifiers listed in the docs menu will be enabled and "just work", so you don't need to think about setting Popper up. The size of Popper including all of its features is about 5 kB minzipped, but it may grow a bit in the future.

Popper Lite (tree-shaking)

If bundle size is important, you'll want to take advantage of tree-shaking. The library is built in a modular way to allow to import only the parts you really need.

import { createPopper } from '@popperjs/core/lib/popper-lite.js';

The Lite version includes the most necessary modifiers that will compute the offsets of the popper, compute and add the positioning styles, and add event listeners. This is close in bundle size to pure CSS tooltip libraries, and behaves somewhat similarly.

However, this does not include the features that makes Popper truly useful.

The two most useful modifiers not included in Lite are preventOverflow and flip:

import { createPopper } from '@popperjs/core/lib/popper-lite.js';
import preventOverflow from '@popperjs/core/lib/modifiers/preventOverflow.js';
import flip from '@popperjs/core/lib/modifiers/flip.js';

const button = document.querySelector('#button');
const tooltip = document.querySelector('#tooltip');

createPopper(button, tooltip, {
  modifiers: [preventOverflow, flip],
});

As you make more poppers, you may be finding yourself needing other modifiers provided by the library.

Distribution targets

Popper is distributed in 3 different versions, in 3 different file formats.

The 3 file formats are:

• esm (works with import syntax — recommended)
• umd (works with <script> tags or RequireJS)
• cjs (works with require() syntax)

The 3 versions are:

• popper: includes all the modifiers (features) in one file (default);
• popper-lite: includes only the minimum amount of modifiers to provide the basic functionality;
• popper-base: doesn't include any modifier, you must import them separately;

Below you can find the size of each version, minified and compressed with the Brotli compression algorithm:

Hacking the library

If you want to play with the library, implement new features, fix a bug you found, or simply experiment with it, this section is for you!

First of all, make sure to have Yarn installed.

Install the development dependencies:

yarn install

And run the development environment:

yarn dev

Then, simply open one the development server web page:

# macOS and Linux
open localhost:5000

# Windows
start localhost:5000

From there, you can open any of the examples (.html files) to fiddle with them.

Now any change you will made to the source code, will be automatically compiled, you just need to refresh the page.

If the page is not working properly, try to go in "Developer Tools > Application > Clear storage" and click on "Clear site data".
To run the examples you need a browser with JavaScript modules via script tag support.

Test Suite

Popper is currently tested with unit tests, and functional tests. Both of them are run by Jest.

Unit Tests

The unit tests use JSDOM to provide a primitive document object API, they are used to ensure the utility functions behave as expected in isolation.

Functional Tests

The functional tests run with Puppeteer, to take advantage of a complete browser environment. They are currently running on Chromium, and Firefox.

You can run them with yarn test:functional. Set the PUPPETEER_BROWSER environment variable to firefox to run them on the Mozilla browser.

The assertions are written in form of image snapshots, so that it's easy to assert for the correct Popper behavior without having to write a lot of offsets comparisons manually.

You can mark a *.test.js file to run in the Puppeteer environment by prepending a @jest-environment puppeteer JSDoc comment to the interested file.

Here's an example of a basic functional test:

/**
 * @jest-environment puppeteer
 * @flow
 */
import { screenshot } from '../utils/puppeteer.js';

it('should position the popper on the right', async () => {
  const page = await browser.newPage();
  await page.goto(`${TEST_URL}/basic.html`);

  expect(await screenshot(page)).toMatchImageSnapshot();
});

You can find the complete jest-puppeteer documentation here, and the jest-image-snapshot documentation here.