JSPM – react-focus-within@1.0.0

Package Exports

react-focus-within

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Readme

A React component that gives you :focus-within behavior.

Why?

Focus management across children is a pain to manage until browsers implement the :focus-within pseudoselector. Use this if you have run into some of these issues:

You want to style a container differently based on if the user has one of its child elements focused (simply using a :focus pseudoselector on the container will not work).
You want to know if a user has left a form but not when a user is simply moving between the form elements inside it.
You want to style an element based on the focus state of two intricately linked elements, but those elements are not near each other on the DOM tree (imagine a button that opens a fixed popup at the root, even though they are physically placed next to each other)

Setup

npm install react-focus-within

Simple Usage

FocusWithin uses children as a function that is passed an object containing focusProps and isFocused, the focusProps should be spread over all children that you want to manage (i.e. any focusable element inside it that can contribute to the focus state), the isFocused boolean is the main payload of the component and will tell you if the user has any of them focused.

import { FocusWithin } from 'react-focus-within'

// the form container will be highlighted red if either the input or the button are focused
const Form = () => (
    <FocusWithin>
        {({ focusProps, isFocused }) => (
            <div
                style={{
                    border: isFocused ? '1px solid red' : 'none'
                }}
            >
                <form>
                    <input {...focusProps} />
                    <button {...focusProps}>Submit</button>
                </form>
            </div>
        )}
    </FocusWithin>
)

Event Handling

FocusWithin emits onFocus and onBlur events when the user enters or leaves its managed children, it will not emit events when a user goes from one managed child to another.

import { FocusWithin } from 'react-focus-within'

// the form container will emit events correctly when a user enters or leaves it
const Form = () => (
    <FocusWithin
        onFocus={() => console.log('Someone is trying to enter things into me!')}
        onBlur={() => console.log('Someone left the form, better validate it!')}
    >
        {({ focusProps, isFocused }) => (
            <div
                style={{
                    border: isFocused ? '1px solid red' : 'none'
                }}
            >
                <form>
                    <input {...focusProps} />
                    <button {...focusProps}>Submit</button>
                </form>
            </div>
        )}
    </FocusWithin>
)

Nesting

Because FocusWithin itself will emit onFocus and onBlur events, you can nest multiple FocusWithins! This can be handy when you want to segregate focus states in a composite UI.

import { FocusWithin } from 'react-focus-within'

const Form = ({ onBlur, onFocus }) => (
    <FocusWithin onBlur={onBlur} onFocus={onFocus}>
        {({ focusProps, isFocused }) => (
            <div
                style={{
                    border: isFocused ? '1px solid red' : 'none'
                }}
            >
                <form>
                    <input {...focusProps} />
                    <button {...focusProps}>Submit</button>
                </form>
            </div>
        )}
    </FocusWithin>
)

// if the user is inside the second form, the overall container will have a background,
// but only the second form will have a red border
const BigForm = () => (
    <FocusWithin>
        {({ focusProps, isFocused }) => (
            <div
                style={{
                    background: isFocused ? 'gray' : 'none'
                }}
            >
                <Form {...focusProps} />
                <Form {...focusProps} />
                <Form {...focusProps} />
            </div>
        )}
    </FocusWithin>
)

Props API

onFocus: () => void - called when focus moves from outside into a managed child. Not called when moving between children
onBlur: () => void - called when focus moves from inside a managed child to outside. Not called when moving between children
children: (renderProps) => JSX.Element - pass in a function as the child of FocusWithin, the shape of renderProps is this:

type renderProps = {
    focusProps: {
        onBlur: Function
        onFocus: Function
    }
    isFocused: boolean
}