React Side Effect  

Create components whose prop changes map to a global side effect.

This is client-side variation of the original react-side-effect, for client-side
components.
It does nothing on server side.

Installation

``
npm install --save react-clientside-effect
`

Use Cases

* Setting document.body.style.margin or background color depending on current screen;
* Firing Flux actions using declarative API depending on current screen;
* Some crazy stuff I haven't thought about.

How's That Different from componentDidUpdate?

It gathers current props across the whole tree before passing them to side effect. For example, this allows you to create component like this:

`js
// RootComponent.js
return (

{this.state.something ? : }

);

// SomeComponent.js
return (





);
`

and let the effect handler merge style from different level of nesting with innermost winning:

`js
import { Component, Children } from 'react';
import PropTypes from 'prop-types';
import withSideEffect from 'react-side-effect';

class BodyStyle extends Component {
render() {
return Children.only(this.props.children);
}
}

BodyStyle.propTypes = {
style: PropTypes.object.isRequired
};

function reducePropsToState(propsList) {
var style = {};
propsList.forEach(function (props) {
Object.assign(style, props.style);
});
return style;
}

function handleStateChangeOnClient(style) {
Object.assign(document.body.style, style);
}

export default withSideEffect(
reducePropsToState,
handleStateChangeOnClient
)(BodyStyle);
`

API

#### withSideEffect: (reducePropsToState, handleStateChangeOnClient, [mapStateOnServer]) -> ReactComponent -> ReactComponent

A higher-order component that, when mounting, unmounting or receiving new props, calls reducePropsToState with props of each mounted instance. It is up to you to return some state aggregated from these props.

On the client, every time the returned component is (un)mounted or its props change, reducePropsToState will be called, and the recalculated state will be passed to handleStateChangeOnClient where you may use it to trigger a side effect.

Usage

Here's how to implement React Document Title (both client and server side) using React Side Effect:

`js
import React, { Children, Component } from 'react';
import PropTypes from 'prop-types';
import withSideEffect from 'react-side-effect';

class DocumentTitle extends Component {
render() {
if (this.props.children) {
return Children.only(this.props.children);
} else {
return null;
}
}
}

DocumentTitle.propTypes = {
title: PropTypes.string.isRequired
};

function reducePropsToState(propsList) {
var innermostProps = propsList[propsList.length - 1];
if (innermostProps) {
return innermostProps.title;
}
}

function handleStateChangeOnClient(title) {
document.title = title || '';
}

export default withSideEffect(
reducePropsToState,
handleStateChangeOnClient
)(DocumentTitle);
``