Clear uses of `setState` would be for UI components that have local display state, but aren&#39;t relevant for the global application. For example a boolean that represents whether a specific dropdown menu is actively displayed doesn&#39;t need to be in global state, so it&#39;s more conveniently controlled by the menu component&#39;s state.

Other examples might include the collapse/expand state of lines in an accordion display of a hierarchy. Or possibly the currently selected tab in tab navigation. However in both of these examples you might still choose to handle UI state globally. For example this would be necessary if you wanted to persist the expand/collapse state in browser storage so that it would be preserved by page refresh.

In practice it&#39;s usually easiest to implement such UI elements with local state, and refactor them into global state as needed.


What&#39;s the most pythonic way to mesh two strings together?

For example:

Input:

    u = &#39;ABCDEFGHIJKLMNOPQRSTUVWXYZ&#39;
    l = &#39;abcdefghijklmnopqrstuvwxyz&#39;

Output:

    &#39;AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz&#39;


Most pythonic way to interleave two strings

I created a docker container from my OS X VM Docker host.  I created it using the run command and created the container based off the `ubuntu:xenial` image off docker hub.

I&#39;m now connected to my container after it&#39;s created and logged in as root and at the command prompt inside my container.

I tried to install homebrew and for some reason, I can&#39;t run the command to install Homebrew:

    ruby -e &quot;$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)&quot;

when I run that I get a bash:

&gt; curl: command not found

Not sure why I&#39;m not able to use curl here inside my container.

Can&#39;t run Curl command inside my Docker Container

Should you ever use `this.setState()` when using redux? Or should you always be dispatching actions and relying on props?

Should you ever use this.setState() when using redux?

<p>Should you ever use <code>this.setState()</code> when using redux? Or should you always be dispatching actions and relying on props?</p>


I&#39;ve noticed that the `reactDOM.renderToString()` method starts to slow down significantly when rendering a large component tree on the server. 

## Background
A bit of background. The system is a fully isomorphic stack. The highest level `App` component renders templates, pages, dom elements, and more components. Looking in the react code, I found it renders ~1500 components (this is inclusive of any simple dom tag that gets treated as a simple component, `&lt;p&gt;this is a react component&lt;/p&gt;`.

In development, rendering ~1500 components takes ~200-300ms. By removing some components I was able to get ~1200 components to render in ~175-225ms. 

In production, renderToString on ~1500 components takes around ~50-200ms.

The time does appear to be linear. No one component is slow, rather it is the sum of many.

## Problem
This creates some problems on the server. The lengthy method results in long server response times. The TTFB is a lot higher than it should be. With api calls and business logic the response should be 250ms, but with a 250ms renderToString it is doubled! Bad for SEO and users. Also, being a synchronous method, `renderToString()` can block the node server and backup subsequent requests (this could be solved by using 2 separate node servers: 1 as a web server, and 1 as a service to solely render react).


## Attempts

Ideally, it would take 5-50ms to renderToString in production. I&#39;ve been working on some ideas, but I&#39;m not exactly sure what the best approach would be.


### Idea 1: Caching components
Any component that is marked as &#39;static&#39; could be cached. By keeping a cache with the rendered markup, the `renderToString()` could check the cache before rendering. If it finds a component, it automatically grabs the string. Doing this at a high level component would save all the nested children component&#39;s mounting. You would have to replace the cached component markup&#39;s react rootID with the current rootID.

### Idea 2: Marking components as simple/dumb
By defining a component as &#39;simple&#39;, react should be able to skip all the lifecycle methods when rendering. React already does this for the core react dom components (`&lt;p/&gt;`, `&lt;h1/&gt;`, etc). Would be nice to extend custom components to use the same optimization.

### Idea 3: Skip components on server-side render
Components that do not need to be returned by the server (no SEO value) could simply be skipped on the server. Once the client loads, set a `clientLoaded` flag to `true` and pass it down to enforce a re-render.


### Closing and other attempts
The only solution I&#39;ve implemented thus far is to reduce the number of components that are rendered on the server. 


Some projects we&#39;re looking at include:

- [React-dom-stream][1]  (still working on implementing this for a test)
- [Babel inline elements][2]  (seems like this is along the lines of Idea 2)

Has anybody faced similar issues? What have you been able to do?
Thanks.


  [1]: https://github.com/aickin/react-dom-stream
  [2]: https://babeljs.io/docs/plugins/transform-react-inline-elements/

React renderToString() Performance and Caching React Components

I am trying to do A SIMPLE using react-router ( **version ^1.0.3** ) to redirect to another view.

    import React from &#39;react&#39;;
    import {Router, Route, Link, RouteHandler} from &#39;react-router&#39;;


    class HomeSection extends React.Component {
    
      static contextTypes = {
        router: PropTypes.func.isRequired
      };
    
      constructor(props, context) {
        super(props, context);
      }
    
      handleClick = () =&gt; {
        console.log(&#39;HERE!&#39;, this.contextTypes);
        // this.context.location.transitionTo(&#39;login&#39;);
      };
    
      render() {
        return (
          &lt;Grid&gt;
            &lt;Row className=&quot;text-center&quot;&gt;          
              &lt;Col md={12} xs={12}&gt;
                &lt;div className=&quot;input-group&quot;&gt;
                  &lt;span className=&quot;input-group-btn&quot;&gt;
                    &lt;button onClick={this.handleClick} type=&quot;button&quot;&gt;
                    &lt;/button&gt;
                  &lt;/span&gt;
                &lt;/div&gt;
              &lt;/Col&gt;
            &lt;/Row&gt;
          &lt;/Grid&gt;
        );
      }
    };
    
    HomeSection.contextTypes = {
      location() {
        React.PropTypes.func.isRequired
      }
    }
    
    export default HomeSection;

all I need is to send the use to &#39;/login&#39; and that&#39;s it.

What can I do ?

errors in console:

&gt;Uncaught ReferenceError: PropTypes is not defined

file with my routes

    // LIBRARY
    /*eslint-disable no-unused-vars*/
    import React from &#39;react&#39;;
    /*eslint-enable no-unused-vars*/
    import {Route, IndexRoute} from &#39;react-router&#39;;
    
    // COMPONENT
    import Application from &#39;./components/App/App&#39;;
    import Contact from &#39;./components/ContactSection/Contact&#39;;
    import HomeSection from &#39;./components/HomeSection/HomeSection&#39;;
    import NotFoundSection from &#39;./components/NotFoundSection/NotFoundSection&#39;;
    import TodoSection from &#39;./components/TodoSection/TodoSection&#39;;
    import LoginForm from &#39;./components/LoginForm/LoginForm&#39;;
    import SignupForm from &#39;./components/SignupForm/SignupForm&#39;;
    
    export default (
        &lt;Route component={Application} path=&#39;/&#39;&gt;
          &lt;IndexRoute component={HomeSection} /&gt;
          &lt;Route component={HomeSection} path=&#39;home&#39; /&gt;
          &lt;Route component={TodoSection} path=&#39;todo&#39; /&gt;
          &lt;Route component={Contact} path=&#39;contact&#39; /&gt;
          &lt;Route component={LoginForm} path=&#39;login&#39; /&gt;
          &lt;Route component={SignupForm} path=&#39;signup&#39; /&gt;
          &lt;Route component={NotFoundSection} path=&#39;*&#39; /&gt;
        &lt;/Route&gt;
    );



How to do a redirect to another route with react-router?

I am trying to set the content of an iframe in a React component but I am not able to do it. I have a component that contains a function which has to be called when the iframe finishes loading. In that function I am setting the content but it doesn&#39;t seem like the onload function is called at all. I am testing it in the Chrome browser. I am trying the following:

    var MyIframe = React.createClass({
        componentDidMount : function(){
            var iframe = this.refs.iframe.getDOMNode();
            if(iframe.attachEvent){
                iframe.attacheEvent(&quot;onload&quot;, this.props.onLoad);
            }else{
                iframe.onload = this.props.onLoad;
            }
        },
        render: function(){
            return &lt;iframe ref=&quot;iframe&quot; {...this.props}/&gt;;
        }
    });
    
    var Display = React.createClass({
        getInitialState : function(){
            return {
                oasData : &quot;&quot;
            };
        },
        iframeOnLoad : function(){
            var iframe = this.refs.bannerIframe;
            iframe.contentDocument.open();
            iframe.contentDocument.write([&#39;&lt;head&gt;&lt;/head&gt;&lt;style&gt;body {margin: 0; overflow: hidden;display:inline-block;} html{ margin: 0 auto; text-align: center;} body &gt; a &gt; img {max-width: 100%; height: inherit;}&#39;, extraCss, &#39;&lt;/style&gt;&lt;/head&gt;&lt;body&gt;&#39;, this.state.oasData.Ad[0].Text, &#39;&lt;/body&gt;&#39;].join(&#39;&#39;));
            iframe.contentDocument.close();
        },
        setOasData : function(data){
            this.setState({
                oasData : JSON.parse(data)
            });
        },
        componentDidMount : function(){
            var url = &quot;getJsonDataUrl&quot;;
    
            var xhttp = new XMLHttpRequest();
            var changeOasDataFunction = this.setOasData;
            xhttp.onreadystatechange = function () {
                if (xhttp.readyState == 4 &amp;&amp; xhttp.status == 200) {
                    changeOasDataFunction(xhttp.responseText);
                }
            };
            xhttp.open(&quot;GET&quot;, url, true);
            xhttp.send();
        },
        render : function(){
            return (
                &lt;MyIframe refs=&quot;bannerIframe&quot; onLoad={this.iframeOnLoad} /&gt;
            );
        }
    });
    
    module.exports = Display;



What am I doing wrong?

How to set iframe content of a react component

In Redux, every change to the store triggers a `notify` on all connected components. This makes things very simple for the developer, but what if you have an application with N connected components, and N is very large?

Every change to the store, even if unrelated to the component, still runs a `shouldComponentUpdate` with a simple `===` test on the `reselect`ed paths of the store. That&#39;s fast, right? Sure, maybe once. But N times, for *every* change? This fundamental change in design makes me question the true scalability of Redux.

As a further optimization, one can batch all `notify` calls using `_.debounce`. Even so, having N `===` tests for every store change *and* handling other logic, for example view logic, seems like a means to an end.

I&#39;m working on a health &amp; fitness social mobile-web hybrid application with millions of users and am transitioning from **Backbone to Redux**. In this application, a user is presented with a swipeable interface that allows them to navigate between different stacks of views, similar to Snapchat, except each stack has infinite depth. In the most popular type of view, an endless scroller efficiently handles the loading, rendering, attaching, and detaching of feed items, like a post. For an engaged user, it is not uncommon to scroll through hundreds or thousands of posts, then enter a user&#39;s feed, then another user&#39;s feed, etc. Even with heavy optimization, the number of connected components can get very large.

Now on the other hand, Backbone&#39;s design allows every view to listen precisely to the models that affect it, reducing N to a constant.

Am I missing something, or is Redux fundamentally flawed for a large app?

Can a React-Redux app really scale as well as, say Backbone? Even with reselect. On mobile

If my React Native app fails to connect to its backend, I show an Alert with an OK button. If this happens, there&#39;s no point in the app continuing to run, so I&#39;d like to shut it down when the button is clicked. How do I do this?

I suspect the key is in AppRegistry but the docs are a bit scant.

How do I exit/shut down a React Native app?

Here is the code in `actions.js`

    export function exportRecordToExcel(record) {
		return ({fetch}) =&gt; ({
			type: EXPORT_RECORD_TO_EXCEL,
			payload: {
				promise: fetch(&#39;/records/export&#39;, {
					credentials: &#39;same-origin&#39;,
					method: &#39;post&#39;,
					headers: {&#39;Content-Type&#39;: &#39;application/json&#39;},
					body: JSON.stringify(data)
				}).then(function(response) {
					return response;
				})
			}
		});
    }

The returned response is an `.xlsx` file. I want the user to be able to save it as a file, but nothing happens. I assume the server is returning the right type of response because in the console it says 

    Content-Disposition:attachment; filename=&quot;report.xlsx&quot;

What I&#39;m I missing? What should I do in the reducer?

How to download fetch response in react as file

The first principle of Redux documentation is:

&gt; The state of your whole application is stored in an object tree within a single store.

And I actually thought that I understand all of the principles well.
But I&#39;m now confused, what does application mean. 

If application means just one of little complicated part in a website and works in just one page, I understand. But what if application means the whole website? Should I use LocalStorage or cookie or something for keeping the state tree? But what if the browser doesn&#39;t support LocalStorage?

I want to know how developers keep their state tree! :)

How can I persist redux state tree on refresh?

I use `axios` for ajax requests and `reactJS` + `flux` for render UI. In my app there is third side timeline (reactJS component). Timeline can be managed by mouse&#39;s scroll. App sends ajax request for the actual data after any scroll event. Problem that processing of request at server can be more slow than next scroll event. In this case app can have several (2-3 usually) requests that already is deprecated because user scrolls further. it is a problem because every time at receiving of new data timeline begins redraw. (Because it&#39;s reactJS + flux) Because of this, the user sees the movement of the timeline back and forth several times. The easiest way to solve this problem, it just abort previous ajax request as in `jQuery`. For example:

        $(document).ready(
        var xhr;
    
        var fn = function(){
            if(xhr &amp;&amp; xhr.readyState != 4){
                xhr.abort();
            }
            xhr = $.ajax({
                url: &#39;ajax/progress.ftl&#39;,
                success: function(data) {
                    //do something
                }
            });
        };
    
        var interval = setInterval(fn, 500);
    );

How to cancel/abort requests in `axios`?

how to cancel/abort ajax request in axios

There is a lot of talk about the latest kid in redux town right now, [redux-saga/redux-saga](https://github.com/redux-saga/redux-saga). It uses generator functions for listening to/dispatching actions.

Before I wrap my head around it, I would like to know the pros/cons of using `redux-saga` instead of the approach below where I&#39;m using `redux-thunk` with async/await.

A component might look like this, dispatch actions like usual.


    import { login } from &#39;redux/auth&#39;;

    class LoginForm extends Component {
      
      onClick(e) {
        e.preventDefault();
        const { user, pass } = this.refs;
        this.props.dispatch(login(user.value, pass.value));
      }
      
      render() {
        return (&lt;div&gt;
            &lt;input type=&quot;text&quot; ref=&quot;user&quot; /&gt;
            &lt;input type=&quot;password&quot; ref=&quot;pass&quot; /&gt;
            &lt;button onClick={::this.onClick}&gt;Sign In&lt;/button&gt;
        &lt;/div&gt;);
      } 
    }

    export default connect((state) =&gt; ({}))(LoginForm);

Then my actions look something like this:

    // auth.js

    import request from &#39;axios&#39;;
    import { loadUserData } from &#39;./user&#39;;

    // define constants
    // define initial state
    // export default reducer

    export const login = (user, pass) =&gt; async (dispatch) =&gt; {
        try {
            dispatch({ type: LOGIN_REQUEST });
            let { data } = await request.post(&#39;/login&#39;, { user, pass });
            await dispatch(loadUserData(data.uid));
            dispatch({ type: LOGIN_SUCCESS, data });
        } catch(error) {
            dispatch({ type: LOGIN_ERROR, error });
        }
    }

    // more actions...

---

    // user.js
    
    import request from &#39;axios&#39;;

    // define constants
    // define initial state
    // export default reducer

    export const loadUserData = (uid) =&gt; async (dispatch) =&gt; {
        try {
            dispatch({ type: USERDATA_REQUEST });
            let { data } = await request.get(`/users/${uid}`);
            dispatch({ type: USERDATA_SUCCESS, data });
        } catch(error) {
            dispatch({ type: USERDATA_ERROR, error });
        }
    }

    // more actions...



Pros/cons of using redux-saga with ES6 generators vs redux-thunk with ES2017 async/await

I have been trying to figure out the best way to manage my react forms. I have tried to use the onChange to fire an action and update my redux store with my form data. I have also tried creating local state and when my form gets submitted I trigger and action and update the redux store. 

How should i manage my controlled input state?

I am using Redux. Should I manage controlled input state in the Redux store or use setState at the component level?

For example from this example:

    export const ADD_TODO = &#39;ADD_TODO&#39;
    export const DELETE_TODO = &#39;DELETE_TODO&#39;
    export const EDIT_TODO = &#39;EDIT_TODO&#39;
    export const COMPLETE_TODO = &#39;COMPLETE_TODO&#39;
    export const COMPLETE_ALL = &#39;COMPLETE_ALL&#39;
    export const CLEAR_COMPLETED = &#39;CLEAR_COMPLETED&#39;

It&#39;s not like you&#39;re saving characters. The variable name is exactly the same as the string, and will never change. I understand making constants if one day you were doing to do something like:

    ADD_TODO = &#39;CREATE_TODO&#39;

but that never happens. So what purpose do these constants serve?

What is the point of the constants in redux?

I am new to the ReactJS world, and would like to know how can I pass active class name to the `&lt;li&gt;` element instead of `&lt;a&gt;(Link)` element.

Now I have this kind of code. The anchor class changes when clicked.

    &lt;li&gt;&lt;IndexLink to=&#39;/&#39; activeclassName=&#39;active&#39;&gt;A&lt;/IndexLink&gt;&lt;/li&gt;
    &lt;li&gt;&lt;Link to=&#39;/b&#39; activeclassName=&#39;active&#39;&gt;B&lt;/Link&gt;&lt;/li&gt;
    &lt;li&gt;&lt;Link to=&#39;/c&#39; activeclassName=&#39;active&#39;&gt;C&lt;/Link&gt;&lt;/li&gt;

But I would like to get something similar to:

    &lt;li activeclassName=&#39;active&#39;&gt;&lt;IndexLink to=&#39;/&#39;&gt;A&lt;/IndexLink&gt;&lt;/li&gt;
    &lt;li activeclassName=&#39;active&#39;&gt;&lt;Link to=&#39;/b&#39;&gt;B&lt;/Link&gt;&lt;/li&gt;
    &lt;li activeclassName=&#39;active&#39;&gt;&lt;Link to=&#39;/c&#39;&gt;C&lt;/Link&gt;&lt;/li&gt;

Thanks in advance

Content Type	Original Author	Original Content on Stackoverflow
Question	Martol1ni	View Question on Stackoverflow
Solution 1 - Reactjs	mjhm	View Answer on Stackoverflow

Should you ever use this.setState() when using redux?

Reactjs Problem Overview

Reactjs Solutions

Solution 1 - Reactjs

Can't run Curl command inside my Docker Container

Most pythonic way to interleave two strings

Attributions