JSPM – react-focus-within@1.2.0

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)

Why Not?

Note that unlike native DOM focus and blur events, the onFocus and onBlur events in React bubble, this means that you can usually get away with those event handlers if you want to simply react to those events, however you will still not be able to apply the :focus pseudoselector unless it is the exact element being focused. Using FocusWithin can save you time:

//without FocusWithin
class Form extends React.Component {
    state = {
        isFocused: false
    }

    render() {
        // color the form if either the input or button are focused
        return (
            <form
                style={{ background: this.state.isFocused ? focusedBackgroundColor : 'none' }}
                onFocus={() => this.setState({ isFocused: true })}
                onBlur={() => this.setState({ isFocused: false })}
            >
                <input />
                <button>Submit</button>
            </form>
        )
    }
}

// with FocusWIthin
const Form = () => (
    <FocusWithin>
        {({ isFocused, focusProps }) => (
            <form {...focusProps} style={{ background: isFocused ? focusedBackgroundColor : 'none' }}>
                <input />
                <button>Submit</button>
            </form>
        )}
    </FocusWithin>
)

// works very well with CSS-in-JS
const StyledForm = withFocusWithin(styled.div`
    background: ${props => (props.isFocused ? focusedBackgroundColor : 'none')};
`)

const Form = () => (
    <StyledForm>
        <input />
        <button>Submit</button>
    </StyledForm>
)

Setup

npm install react-focus-within

import FocusWithin from 'react-focus-within'
import { FocusWithin } from 'react-focus-within'
import { withFocusWithin } from '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
                {...focusProps}
                style={{
                    border: isFocused ? '1px solid red' : 'none'
                }}
            >
                <form>
                    <input />
                    <button>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. You will not need this much power most of the time unless you need precise timing and frequency of onFocus and onBlur event emissions.

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

// the form container will only emit onFocus and onBlur if they completely leave the form
// it will not emit either events if they are moving focus between the input and the button
// which is different than the default React behavior
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'
import Form from 'example-above'

// 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
                {...focusProps}
                style={{
                    background: isFocused ? 'gray' : 'none'
                }}
            >
                <Form />
                <Form />
                <Form />
            </div>
        )}
    </FocusWithin>
)

Currently, mixing managed FocusWithins and other managed component types is not supported:

const MixedForm = () => (
    <FocusWithin>
        {({ focusProps, isFocused }) => (
            <div
                style={{
                    background: isFocused ? 'gray' : 'none'
                }}
            >
                {/* this will not work correctly */}
                <Form {...focusProps} />
                <Form {...focusProps} />
                <input {...focusProps} />

                {/* these will work */}
                <Form {...focusProps} />
                <Form {...focusProps} />
                <Form {...focusProps} />

                {/* these will work too */}
                <input {...focusProps} />
                <input {...focusProps} />
                <input {...focusProps} />
            </div>
        )}
    </FocusWithin>
)

You should not run into this problem most of the time; you can just spread focusProps to the container that you want to style since onFocus and onBlur will bubble up to it.

If you still need to individually manage each child, you will have to wrap the non-FocusWithin managed children inside one. The module exports an HOC function called withFocusWithin and a static method in FocusWithin called wrapComponent (they are the same) to help with that:

const WrappedNativeInput = FocusWithin.wrapComponent('input') // same as withFocusWithin('input')
const WrappedOtherComponent = FocusWithin.wrapComponent(OtherComponent) // same as withFocusWithin(OtherComponent)

const OkayMixedForm = () => (
    <FocusWithin>
        {({ focusProps, isFocused }) => (
            <div
                style={{
                    background: isFocused ? 'gray' : 'none'
                }}
            >
                <Form {...focusProps} />
                <WrappedNativeInput {...focusProps} />
                <WrappedOtherComponent {...focusProps} />

                {/* equivalent to: */}
                <Form {...focusProps} />
                <FocusWithin {...focusProps}>{({ focusProps }) => <input {...focusProps} />}</FocusWithin>
                <FocusWithin {...focusProps}>{({ focusProps }) => <OtherComponent {...focusProps} />}</FocusWithin>
            </div>
        )}
    </FocusWithin>
)

Why is this? This is due to how native or passthrough onBlur and onFocus events are triggered immediately by React, whereas the onBlur and onFocus events triggered by other FocusWithin components are delayed by a setTimeout to determine if focus actually has changed inside it, which can lead to out-of-order event triggering when the two are mixed. Again, you should not be encountering this in common usage.

Props API

onFocus: (event) => void - called when focus moves from outside into a managed child. Not called when moving between children.
onBlur: (event) => 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
}

⚠️ If you are wrapping the event handlers in focusProps before applying it to managed children, make sure to pass the native event object back to the original onBlur and onFocus events, FocusWithin relies on this to determine if an event was emitted from a native DOM element or a nested FocusWithin element

Other API

withFocusWithin(Component) => ReactComponent - use as a quick wrapper around a container component, the container element will receive an isFocused prop if any of its children are focused. The isFocused prop will not be passed in if you are wrapping a native DOM component, since it does not understand isFocused as an attribute.
FocusWithin.wrapComponent - this is exactly the same as withFocusWithin