You can use exec to run from script

    import {series} from &#39;async&#39;;
    const {exec} = require(&#39;child_process&#39;);
    
    series([
     () =&gt; exec(&#39;npm run dev&#39;),
     () =&gt; exec(&#39;npm run test&#39;)
    ]); 

Just install `npm`:

    npm install npm

Then in your program:

    npm.commands.run(&#39;dev&#39;, (err) =&gt; { ... });

See the source for more info. The `npm.command` object is an unofficial API for npm. Note that using `exec` or `spawn` to execute `npm` is safer, since the API is unofficial.


Here is a solution that should work reliably across all platforms. It&#39;s also very concise. Put this into `build.js`, then run `node build`.

    const {execSync} = require(&#39;child_process&#39;)

    execSync(&quot;npm run clean&quot;)
    execSync(&quot;npm run minify&quot;)
    execSync(&quot;npm run build_assets&quot;)

It will immediately abort on abnormal npm termination.


The npm documentation recommends using `shelljs`:

```
var shell = require(&quot;shelljs&quot;);

shell.exec(&quot;echo shell.exec works&quot;);
shell.exec(&quot;npm run dev&quot;);
```

See https://blog.npmjs.org/post/118810260230/building-a-simple-command-line-tool-with-npm.html

Use [PM2][1], it is really usefull and easy...
```
npm install pm2
```

```
const pm2 = require(&#39;pm2&#39;);

pm2.start({
    script: &#39;npm -- run monitorTheWeather&#39;,
    autorestart : false 
  }, (err, apps) =&gt; {
    pm2.disconnect()
    if (err) { throw err }
  })
```


  [1]: https://github.com/Unitech/pm2

I have some template files that contain a few variable strings each, I&#39;d like to build a very simple input form with Electron (https://www.electronjs.org/) and I want to save the composed output file on the user&#39;s computer.

Is there any module I can use to let Electron save files locally?

Saving files locally with electron

When you use ***[BeautifulSoup][1]*** to scrape a certain part of a website, you can use 

 - `soup.find()` and `soup.findAll()` or
 - `soup.select()`.

Is there a difference between the `.find()` and the `.select()` methods?
(e.g. In performance or flexibility, etc.) Or are they the same?


  [1]: https://www.crummy.com/software/BeautifulSoup/bs4/doc/

Beautifulsoup : Difference between .find() and .select()

I have some custom testing script, which I can run with `npm run test` command, which executes some Node script for starting e2e/unit tests. But before it I must start webpack dev server with `npm run dev` (it&#39;s a some custom Node script too, details doesn&#39;t matter) in other terminal window. So, I want to omit `npm run dev` manually executing and move it to custom `npm run test` script, i.e. I want to execute webpack dev server programmatically in Node script. How can I execute `npm run dev` programmatically using Node script and stop it then? Thanks in advance! 

    &quot;dev&quot;: &quot;node node_modules/webpack-dev-server/bin/webpack-dev-server.js --host 0.0.0.0 --history-api-fallback --debug --inline --progress --config config/config.js&quot;

How to execute &#39;npm run&#39; command programmatically?

I have some custom testing script, which I can run with <code>npm run test</code> command, which executes some Node script for starting e2e/unit tests. But before it I must start webpack dev server with <code>npm run dev</code> (it's a some custom Node script too, details doesn't matter) in other terminal window. So, I want to omit <code>npm run dev</code> manually executing and move it to custom <code>npm run test</code> script, i.e. I want to execute webpack dev server programmatically in Node script. How can I execute <code>npm run dev</code> programmatically using Node script and stop it then? Thanks in advance!
<pre><code class="hljs language-json">"dev": "node node_modules/webpack-dev-server/bin/webpack-dev-server.js --host 0.0.0.0 --history-api-fallback --debug --inline --progress --config config/config.js"
</code></pre>

I am in the process of implementing a filterable list with React. The structure of the list is as shown in the image below.

[![enter image description here][1]][1]

**PREMISE**

Here&#39;s a description of how it is supposed to work:

* The state resides in the highest level component, the `Search` component.
* The state is described as follows:
&lt;pre&gt;
{
    visible : boolean,
    files : array,
    filtered : array,
    query : string,
    currentlySelectedIndex : integer
}
&lt;/pre&gt;

* `files ` is a potentially very large, array containing file paths (10000 entries is a plausible number).
* `filtered` is the filtered array after the user types at least 2 characters. I know it&#39;s derivative data and as such an argument could be made about storing it in the state but it is needed for
* `currentlySelectedIndex` which is the index of the currently selected element from the filtered list.

* User types more than 2 letters into the `Input` component, the array is filtered and for each entry in the filtered array a `Result` component is rendered
* Each `Result` component is displaying the full path that partially matched the query, and the partial match part of the path is highlighted. For example the DOM of a Result component, if the user had typed &#39;le&#39; would be something like this :

  `&lt;li&gt;this/is/a/fi&lt;strong&gt;le&lt;/strong&gt;/path&lt;/li&gt;`
* If the user presses the up or down keys while the `Input` component is focused the `currentlySelectedIndex` changes based on the `filtered` array. This causes the `Result` component that matches the index to be marked as selected causing a re-render

**PROBLEM**

Initially I tested this with a small enough array of `files`, using the development version of React, and all worked fine. 

The problem appeared when I had to deal with a `files` array as big as 10000 entries. Typing 2 letters in the Input would generate a big list and when I pressed the up and down keys to navigate it it would be very laggy.

At first I did not have a defined component for the `Result` elements and I was merely making the list on the fly, on each render of the `Search` component, as such:


    results  = this.state.filtered.map(function(file, index) {
        var start, end, matchIndex, match = this.state.query;
    
         matchIndex = file.indexOf(match);
         start = file.slice(0, matchIndex);
         end = file.slice(matchIndex + match.length);
    
         return (
             &lt;li onClick={this.handleListClick}
                 data-path={file}
                 className={(index === this.state.currentlySelected) ? &quot;valid selected&quot; : &quot;valid&quot;}
                 key={file} &gt;
                 {start}
                 &lt;span className=&quot;marked&quot;&gt;{match}&lt;/span&gt;
                 {end}
             &lt;/li&gt;
         );
    }.bind(this));

As you can tell, every time the `currentlySelectedIndex` changed, it would cause a re-render and the list would be re-created each time. I thought that since I had set a `key` value on each `li` element React would avoid re-rendering every other `li` element that did not have its `className` change, but apparently it wasn&#39;t so.

I ended up defining a class for the `Result` elements, where it explicitly checks whether each `Result` element should re-render based on whether it was previously selected and based on the current user input :

    var ResultItem = React.createClass({
        shouldComponentUpdate : function(nextProps) {
            if (nextProps.match !== this.props.match) {
                return true;
            } else {
                return (nextProps.selected !== this.props.selected);
            }
        },
        render : function() {
            return (
                &lt;li onClick={this.props.handleListClick}
                    data-path={this.props.file}
                    className={
                        (this.props.selected) ? &quot;valid selected&quot; : &quot;valid&quot;
                    }
                    key={this.props.file} &gt;
                    {this.props.children}
                &lt;/li&gt;
            );
        }
    });

And the list is now created as such: 

    results = this.state.filtered.map(function(file, index) {
        var start, end, matchIndex, match = this.state.query, selected;
    
        matchIndex = file.indexOf(match);
        start = file.slice(0, matchIndex);
        end = file.slice(matchIndex + match.length);
        selected = (index === this.state.currentlySelected) ? true : false
    
        return (
            &lt;ResultItem handleClick={this.handleListClick}
                data-path={file}
                selected={selected}
                key={file}
                match={match} &gt;
                {start}
                &lt;span className=&quot;marked&quot;&gt;{match}&lt;/span&gt;
                {end}
            &lt;/ResultItem&gt;
        );
    }.bind(this));
    }

This made performance *slightly* better, but it&#39;s still not good enough. Thing is when I tested on the production version of React things worked buttery smooth, no lag at all. 

**BOTTOMLINE**

**Is such a noticeable discrepancy between development and production versions of React normal?**

**Am I understanding/doing something wrong when I think about how React manages the list?** 

**UPDATE 14-11-2016**

I have found this presentation of Michael Jackson, where he tackles an issue very similar to this one: https://youtu.be/7S8v8jfLb1Q?t=26m2s

The solution is very similar to the one proposed by AskarovBeknar&#39;s [answer](https://stackoverflow.com/a/38193164/4651083), below

**UPDATE 14-4-2018**

Since this is apparently a popular question and things have progressed since the original question was asked, while I do encourage you to watch the video linked above, in order to get a grasp of a virtual layout, I also encourage you to use the [React Virtualized](https://github.com/bvaughn/react-virtualized) library if you do not want to re-invent the wheel. 


  [1]: http://i.stack.imgur.com/lTcZm.png

Big list performance with React

Many examples of this on here but can&#39;t seem to find any for react. I have managed to convert the vanilla js to react but getting [an error][1].

The answer looks simple enough so here I go in react:

    getInitialState: function(){
      return{file: []}
    },
    
    _onChange: function(){
      // Assuming only image
      var file = this.refs.file.files[0];
      var reader = new FileReader();
      var url = reader.readAsDataURL(file);
      console.log(url) // Would see a path?
      // TODO: concat files for setState
    },
    
    render: function(){
     return(
      &lt;div&gt;
        &lt;form&gt;
          &lt;input 
            ref=&quot;file&quot; 
            type=&quot;file&quot; 
            name=&quot;user[image]&quot; 
            multiple=&quot;true&quot;
            onChange={this._onChange}/&gt;
         &lt;/form&gt;
        {/* Only show first image, for now. */}
        &lt;img src={this.state.file[0} /&gt;
      &lt;/div&gt;
     )
    };

Basically all answers I have seen show something like what I have. Any difference in React app?

Regarding answer:

[![enter image description here][2]][2]


  [1]: https://stackoverflow.com/questions/32508191/uncaught-typeerror-failed-to-execute-readasdataurl-on-filereader-parameter
  [2]: http://i.stack.imgur.com/o08oe.png

Get image preview before uploading in React

Is there a syntax using ES6 or ES7 or babel which will allow me to easily bundle together many groups of sub files? 

E.g., given:

    ./action_creators/index.js
    ./action_creators/foo_actions.js
    ./action_creators/bar_actions.js

Have index.js import foo and bar actions, then re-export them, so I can

    import {FooAction, BarAction} from &#39;./action_creators/index.js&#39;

I don&#39;t want to have to remember / change references if I were to change which file I&#39;ve organized the objects themselves into. 



ES6 `export * from import`?

I have a wrapper that catches the last result of a promise, formats it and outputs the data:

	req.resolve = (promise) =&gt; {
		return promise.then(() =&gt; {
				res.json(req.user);
			}).catch(Sequelize.ValidationError, err =&gt; {
			// respond with validation errors
			return res.status(422).send(err.errors);
		}).catch(err =&gt; {
			// every other error
			return res.status(400).send({ message: err.message });
		});
	};

In one view, I don&#39;t have a promise, all that happens is that the auth-function triggers adds req.user and triggers `done()`.  

I tried adding a promise like this, but it doesn&#39;t get resolved.

    app.get(&#39;/user/me&#39;, auth,
    	(req, res, next) =&gt; {
    		req.resolve(new Promise());
    	});

Create an empty promise that just fulfills?

I&#39;m trying to develop a class on the top of the mongoose with my custom methods, so I extended the mongoose with my own class but when I invoke to create a new car method it works but its strip and error, here I let you see what I&#39;m trying to do.

I&#39;m getting this warning

    (node:3341) DeprecationWarning: Mongoose: mpromise (mongoose&#39;s default promise library) is deprecated, plug in your own promise library instead: http://mongoosejs.com/docs/promises.html

after I do

    driver.createCar({
          carName: &#39;jeep&#39;,
          availableSeats: 4,
        }, callback);
driver is an instance of Driver class

    const carSchema = new Schema({
      carName: String,
      availableSeats: Number,
      createdOn: { type: Date, default: Date.now },
    });
    const driverSchema = new Schema({
     email: String,
     name: String,
     city: String,
     phoneNumber: String,
     cars: [carSchema],
     userId: {
       type: Schema.Types.ObjectId,
       required: true,
     },
    createdOn: { type: Date, default: Date.now },
    });
    const DriverModel = mongoose.model(&#39;Driver&#39;, driverSchema);

    class Driver extends DriverModel {
      getCurrentDate() {
      return moment().format();
    }
    create(cb) {
      // save driver
      this.createdOn = this.getCurrentDate();
      this.save(cb);
    }
    remove(cb) {
      super.remove({
      _id: this._id,
     }, cb);
    }
    createCar(carData, cb) {
      this.cars.push(carData);
      this.save(cb);
    }
    getCars() {
      return this.cars;
     }
    }
any thoughts about what Im doing wrong?

(node:3341) DeprecationWarning: Mongoose: mpromise

I am using npm &#39;isomorphic-fetch&#39; to send requests. The problem I am experiencing is I am unable to set the content-type of the request header.

I set a content type of application/json , however the request header are being set to text/plain.

    import &#39;isomorphic-fetch&#39;;
    
      sendRequest(url, method, body) {
        const options = {
          method: method,
          headers:{&#39;content-type&#39;: &#39;application/json&#39;},
          mode: &#39;no-cors&#39;
        };
    
        options.body = JSON.stringify(body);
    
        return fetch(url, options);
      }

When I examine the request in my browser the content type is o :

    content-type:text/plain;charset=UTF-8

Can anyone explain why I am unable to set this property?




How to set the content-type of request header when using Fetch APi

I installed node.js and npm to my centOS 7 server. But i have problems with pm2.
Actually real problem is i don&#39;t have experiences in linux and i don&#39;t know how to change path.
Here is folder structure.

    * bin
    * code
    * error_docs
    * httpdocs
    * lib64
    * logs
    * tmp
    * var
    * chat(my node.js folder)
        * node_modules
            * pm2
            * sockjs
        * server.js
    * dev
    * etc
    * lib
    * local
    * sbin
    * usr

I entered folder by typing `cd chat` and installed pm2 with `npm install pm2`.

After that I tried use pm2 for my server.js by typing `pm2 server.js` server returns &quot;pm2 command not found&quot;. I can use node.js without any problem but pm2 not working.

How can i solve this?

PM2 command not found

**Edit**

 1. Pattern that keep on retrying until the promise resolves (with `delay` and
    `maxRetries`). 
 2. Pattern that keeps on retrying until the condition
    meets on the result (with `delay` and
    `maxRetries`).
 3. A memory efficient dynamic Pattern with unlimited retries (`delay` provided).


**Code for #1.** Keeps on retrying until promise resolves (any improvements community for the language etc?)

    Promise.retry = function(fn, times, delay) {
        return new Promise(function(resolve, reject){
            var error;
            var attempt = function() {
                if (times == 0) {
                    reject(error);
                } else {
                    fn().then(resolve)
                        .catch(function(e){
                            times--;
                            error = e;
                            setTimeout(function(){attempt()}, delay);
                        });
                }
            };
            attempt();
        });
    };


Use

    work.getStatus()
        .then(function(result){ //retry, some glitch in the system
            return Promise.retry(work.unpublish.bind(work, result), 10, 2000);
        })
        .then(function(){console.log(&#39;done&#39;)})
        .catch(console.error);


----------


**Code for #2** keep on retrying until a condition meets on the `then` result in a reusable way (condition is what will vary).

    work.publish()
        .then(function(result){
            return new Promise(function(resolve, reject){
                var intervalId = setInterval(function(){
                    work.requestStatus(result).then(function(result2){
                        switch(result2.status) {
                            case &quot;progress&quot;: break; //do nothing
                            case &quot;success&quot;: clearInterval(intervalId); resolve(result2); break;
                            case &quot;failure&quot;: clearInterval(intervalId); reject(result2); break;
                        }
                    }).catch(function(error){clearInterval(intervalId); reject(error)});
                }, 1000);
            });
        })
        .then(function(){console.log(&#39;done&#39;)})
        .catch(console.error);


  [1]: https://en.wikipedia.org/wiki/Software_design_pattern
  [2]: https://github.com/icodeforlove/promise-retryer
  [3]: https://gist.github.com/domenic/2936696

Content Type	Original Author	Original Content on Stackoverflow
Question	malcoauri	View Question on Stackoverflow
Solution 1 - Javascript	Foysal Osmany	View Answer on Stackoverflow
Solution 2 - Javascript	mzedeler	View Answer on Stackoverflow
Solution 3 - Javascript	user1050755	View Answer on Stackoverflow
Solution 4 - Javascript	zr0gravity7	View Answer on Stackoverflow
Solution 5 - Javascript	Joris Ceelen	View Answer on Stackoverflow

How to execute 'npm run' command programmatically?

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

Solution 2 - Javascript

Solution 3 - Javascript

Solution 4 - Javascript

Solution 5 - Javascript

Beautifulsoup : Difference between .find() and .select()

Saving files locally with electron

Attributions