In your `.babelrc` file, change 

    { &quot;presets&quot;: [&quot;env&quot;] } 

to 

    { &quot;presets&quot;: [&quot;@babel/preset-env&quot;] }

(and install that package if you haven&#39;t already).

In your `.babelrc` you are still referencing the package `babel-preset-env` (which is for 6.x), you want to reference `@babel/preset-env` instead (which is for 7.x).

&gt;https://github.com/babel/babel/issues/6186#issuecomment-366556833

**Note:** you should also make this change in `webpack.config.js` if it is there as well.

Here is the sample webpack config section where you should change the preset:

    use: {
      loader: &#39;babel-loader&#39;,
      options: {
        // Here you should change &#39;env&#39; to &#39;@babel/preset-env&#39;
        presets: [&#39;@babel/preset-env&#39;],
      },
    },

I&#39;m trying to copy files from Kubernetes Pods to my local system. I am getting the below error while running following command: 

    kubectl cp aks-ssh2-6cd4948f6f-fp9tl:/home/azureuser/test.cap ./test.cap

Output:

&gt; tar: home/azureuser/test: Cannot stat: No such file or directory tar:
&gt; Exiting with failure status due to previous errors error:
&gt; home/azureuser/test no such file or directory

I could see the file under above given path. I am really confused.

Could you please help me out?

How to copy files from kubernetes Pods to local system

Edit: Pylance seems to be _much_ better at this and has so far resolved all problems with the previous Python language server from Microsoft.

I&#39;m using VS Code and it&#39;s wonderful is all areas but code completion, where it is usually just too slow to be of any use. This example shows how long intellisense took to to find a local variable, and this is only after it was prompted to do so after I hit ctrl+enter.

[![enter image description here][1]][1]

I&#39;ve not been able to find a solution to this as of yet, so I am here to ask if anyone else has had a similar issue and ask how they have overcome it. 


  [1]: https://i.stack.imgur.com/k0MsN.gif

Visual Studio Code Intellisense is very slow - Is there anything I can do?

I just upgraded to [Babel 7](https://babeljs.io/docs/en/index.html) (from 6) by running these commands:


    npm remove babel-cli
    npm install --save-dev @babel/cli @babel/core @babel/preset-env

Here is my `.babelrc` file:

    { &quot;presets&quot;: [&quot;env&quot;] }

Then I ran:

    babel js/src --out-dir js/dist

And it results in:

    TypeError: Cannot read property &#39;bindings&#39; of null
        at Scope.moveBindingTo (/xyz/node_modules/@babel/traverse/lib/scope/index.js:867:13)
        at BlockScoping.updateScopeInfo (/xyz/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:364:17)
        at BlockScoping.run (/xyz/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:330:12)
        at PluginPass.BlockStatementSwitchStatementProgram (/xyz/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:70:24)
        at newFn (/xyz/node_modules/@babel/traverse/lib/visitors.js:193:21)
        at NodePath._call (/xyz/node_modules/@babel/traverse/lib/path/context.js:53:20)
        at NodePath.call (/xyz/node_modules/@babel/traverse/lib/path/context.js:40:17)
        at NodePath.visit (/xyz/node_modules/@babel/traverse/lib/path/context.js:88:12)
        at TraversalContext.visitQueue (/xyz/node_modules/@babel/traverse/lib/context.js:118:16)
        at TraversalContext.visitSingle (/xyz/node_modules/@babel/traverse/lib/context.js:90:19)

What did I do wrong?

Upgrade to Babel 7: Cannot read property &#39;bindings&#39; of null

I just upgraded to <a href="https://babeljs.io/docs/en/index.html" target="_blank" rel="noopener noreferrer">Babel 7</a> (from 6) by running these commands:
<pre><code class="hljs language-scss">npm remove babel-cli
npm install --save-dev @babel/cli @babel/core @babel/preset-env
</code></pre>
Here is my <code>.babelrc</code> file:
<pre><code class="hljs language-json">{ "presets": ["env"] }
</code></pre>
Then I ran:
<pre><code class="hljs language-bash">babel js/src --out-dir js/dist
</code></pre>
And it results in:
<pre><code class="hljs language-less">TypeError: Cannot read property 'bindings' of null
 at Scope.moveBindingTo (/xyz/node_modules/@babel/traverse/lib/scope/index.js:867:13)
 at BlockScoping.updateScopeInfo (/xyz/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:364:17)
 at BlockScoping.run (/xyz/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:330:12)
 at PluginPass.BlockStatementSwitchStatementProgram (/xyz/node_modules/babel-plugin-transform-es2015-block-scoping/lib/index.js:70:24)
 at newFn (/xyz/node_modules/@babel/traverse/lib/visitors.js:193:21)
 at NodePath._call (/xyz/node_modules/@babel/traverse/lib/path/context.js:53:20)
 at NodePath.call (/xyz/node_modules/@babel/traverse/lib/path/context.js:40:17)
 at NodePath.visit (/xyz/node_modules/@babel/traverse/lib/path/context.js:88:12)
 at TraversalContext.visitQueue (/xyz/node_modules/@babel/traverse/lib/context.js:118:16)
 at TraversalContext.visitSingle (/xyz/node_modules/@babel/traverse/lib/context.js:90:19)
</code></pre>
What did I do wrong?

Hi I&#39;m starting with javascript and react-native and I&#39;m trying to figure out this problem for hours now. Can someone explain me how to get all the documents from firestore collection ?

I have been trying this: 

    async getMarkers() {
      const events = await firebase.firestore().collection(&#39;events&#39;).get()
        .then(querySnapshot =&gt; {
          querySnapshot.docs.map(doc =&gt; {
            console.log(&#39;LOG 1&#39;, doc.data());
            return doc.data();
          });
        });
      console.log(&#39;LOG 2&#39;, events);
      return events;
    }

Log 1 prints all the objects(one by one) but log 2 is undefined, why ?

Getting all documents from one collection in Firestore

I&#39;m using node.js and puppeteer to get some data. Some of the files I&#39;m opening are quite large ... and then I get an error:

Error: 

	our error { TimeoutError: Navigation Timeout Exceeded: 30000ms exceeded
	    at Promise.then (/project/node_modules/puppeteer/lib/NavigatorWatcher.js:74:21)
	    at &lt;anonymous&gt; name: &#39;TimeoutError&#39; }
	
How can I ignore it or set a higher timeout?	
	
That&#39;s my script:	

	await page.goto(&#39;url&#39;+tableCell04Val, {waitUntil: &#39;load&#39;});
	

Node.js puppeteer - How to set navigation timeout?

Any ideas on this code

    jest.useFakeTimers() 

    it(&#39;simpleTimer&#39;, async () =&gt; {
      async function simpleTimer(callback) {
        await callback()    // LINE-A without await here, test works as expected.
        setTimeout(() =&gt; {
          simpleTimer(callback)
        }, 1000)
      }

      const callback = jest.fn()
      await simpleTimer(callback)
      jest.advanceTimersByTime(8000)
      expect(callback).toHaveBeenCalledTimes(9)
    }
```

Failed with


    Expected mock function to have been called nine times, but it was called two times.


However, If I remove `await` from LINE-A, the test passes. 

Does Promise and Timer not work well?

I think the reason maybe jest is waiting for second promise to resolve.


Jest: Timer and Promise don&#39;t work well. (setTimeout and async function)

I am working on a project where I have to pass data from one page to another.
For example, I have `data` on the first page.
 

    let data = [
      {id:1, name:&#39;Ford&#39;, color:&#39;Red&#39;},
      {id:2, name:&#39;Hyundai&#39;, color:&#39;Blue&#39;}
    ]

Here is the first component page where I render this list of data with the name. 

    class ListDetail extends Component {
        constructor();
        handleClick(data){
        console.log(data);
      }
      render() {
        return (
          &lt;div&gt;
            &lt;Hello name={this.state.name} /&gt;
            &lt;ul&gt;
              {data.map((data,i) =&gt; {
                return &lt;li onClick={this.handleClick.bind(this,data)}&gt;{data.name}&lt;/li&gt;
              })}
            &lt;/ul&gt;
          &lt;/div&gt;
        );
      }
    }

I want to pass this data to the next page where I need this data and more data than this. I am using React Router 4. Any suggestion or help would be helpful.


React-router - How to pass data between pages in React?

I am trying to convert the below date to a javascript Date() object. When I get it back from the server, it is a Timestamp object, 

**Screenshot from Firebase Firestore console:**

[![enter image description here][1]][1]





When I try the following on a list of objects returned from firestore:

      list.forEach(a =&gt; {
        var d = a.record.dateCreated;
        console.log(d, new Date(d), Date(d))
      })



**I get this output:**
[![enter image description here][2]][2]


Clearly the Timestamps are all different, and are not all the same date of Sept 09, 2018 (which happens to be today). I&#39;m also not sure why `new Date(Timestamp)` results in an `invalid date`. I&#39;m a bit of a JS newbie, am I doing something wrong with the dates or timestamps?


  [1]: https://i.stack.imgur.com/Dz7gE.png
  [2]: https://i.stack.imgur.com/H5NEW.png


How do I convert a Firestore date/Timestamp to a JS Date()?

I&#39;m facing this weird issue in NodeJS when using with Passport.js, Express and Mongoose. Basically, I get an error saying &quot;Cannot set headers after they are sent to the client&quot; even though I don&#39;t send more than one header.

I&#39;ve read other posts and tried them out as well, and none of them worked.

 - 
https://stackoverflow.com/questions/43055600/app-get-is-there-any-difference-between-res-send-vs-return-res-send
 - https://stackoverflow.com/questions/49740710/error-err-http-headers-sent-cannot-set-headers-after-they-are-sent-to-the-cli
 - https://stackoverflow.com/questions/47753743/cannot-set-headers-after-they-are-sent-to-the-client

I&#39;ve dug through github issues and I can&#39;t seem to find a solution. I get the problem that this error is triggered when I send multiple response headers, but the fact is that I am not sending multiple headers. It seems just weird.

This is my stack trace:

    

&gt; (node:9236) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.

&gt; Server Running on port 5000  
&gt; MongoDB Connected Error  
&gt;[ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the
&gt; client  
&gt; &amp;nbsp;&amp;nbsp;at validateHeader (_http_outgoing.js:503:11)  
&gt; &amp;nbsp;&amp;nbsp; at ServerResponse.setHeader (_http_outgoing.js:510:3)  
&gt; &amp;nbsp;&amp;nbsp; at ServerResponse.header (/Users/lourdesroashan/code/github/devlog/node_modules/express/lib/response.js:767:10)  
&gt; &amp;nbsp;&amp;nbsp; at ServerResponse.json (/Users/lourdesroashan/code/github/devlog/node_modules/express/lib/response.js:264:10)  
&gt; &amp;nbsp;&amp;nbsp; at Profile.findOne.then.profile (/Users/lourdesroashan/code/github/devlog/routes/api/profile.js:27:30)  
&gt; &amp;nbsp;&amp;nbsp; at &amp;lt;anonymous&amp;gt;

This is my server code:

    router.get(&quot;/userprofile&quot;, passport.authenticate(&#39;jwt&#39;, { session: false }), (req, res) =&gt; {
    
      Profile.findOne({ user: req.user.id }).then(profile =&gt; {
        if (!profile) {
          return res.status(404).json({ error: &quot;No Profile Found&quot; });
        }
        else {
          res.json(profile);
        }
      }).catch(err =&gt; {
        console.log(err);
      })
    });

I understand what the error means, but from what I know, I don&#39;t think I am sending multiple headers, I even checked by console.log that only one of the blocks is run.

Thank you so much in advance! :)

Full Code at: https://github.com/lourdesr/devlog


**EDIT:**

I figured it out. It was a problem in my passport.js while trying to get the authenticated user. I forgot to use &#39;return&#39; on the &#39;done&#39; method, which had caused it. Just added the return statement and it worked!

ERR_HTTP_HEADERS_SENT: Cannot set headers after they are sent to the client

Getting error when script move to other server. 

&gt;(node:15707) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.  

Current Versions:  

    Ubuntu 16.04.4 LTS  
    Node - v10.9.0  
    NPM - 6.2.0  

Previous Version:

    Ubuntu 14.04.3 LTS
    NPM - 3.10.10
    Node - v6.10.3
&lt;br&gt;

    exports.basicAuthentication = function (req, res, next) {
        console.log(&quot;basicAuthentication&quot;);
        if (!req.headers.authorization) {
            return res.status(401).send({
                message: &quot;Unauthorised access&quot;
            });
        }
        var auth = req.headers.authorization;
        var baseAuth = auth.replace(&quot;Basic&quot;, &quot;&quot;);
        baseAuth = baseAuth.trim();
        var userPasswordString = new Buffer(baseAuth, &#39;base64&#39;).toString(&#39;ascii&#39;);
        var credentials = userPasswordString.split(&#39;:&#39;);

        var username = credentials[0] !== undefined ? credentials[0] : &#39;&#39;;
        var password = credentials[1] !== undefined ? credentials[1] : &#39;&#39;;
        var userQuery = {mobilenumber: username, otp: password};
        console.log(userQuery);
        User.findOne(userQuery).exec(function (err, userinfo) {
            if (err || !userinfo) {
                 return res.status(401).send({
                    message: &quot;Unauthorised access&quot;
                 });
            } else {
                req.user = userinfo;
                next();
            }
        });

     }




DeprecationWarning: Buffer() is deprecated due to security and usability issues when I move my script to another server

I want to update a doc like this:

    db.collection(&#39;users&#39;).doc(user_id).update({foo:&#39;bar&#39;})

However, if the doc user_id does not exists, the above code will throw an error.
Hence, how to tell Firestore to create the student if not exists, in other word, behave like this:

    db.collection(&#39;users&#39;).doc(user_id).set({foo:&#39;bar&#39;})

FireStore create a document if not exist

I am setting an [invisible reCAPTCHA][1] in my web application and having trouble verifying the user&#39;s response. (even though I am passing the correct POST parameters)

I am programmatically invoking the challenge by calling `grecaptcha.execute();` on the client-side. And submitting the form afterwards (`registrationForm.submit();`) using the recaptcha callback:

&lt;!-- language: lang-html --&gt;

    &lt;div class=&quot;g-recaptcha&quot;
      data-sitekey=&quot;SITE_KEY&quot;
      data-callback=&quot;onSubmit&quot;
      data-size=&quot;invisible&quot;&gt;
    &lt;/div&gt;

Now after reading [_&quot;Verifying the user&#39;s response&quot;_][2] documentation, I figured that the response token is passed as a POST parameter to `g-recaptcha-response`:

&gt; For web users, you can get the user’s response token in one of three ways:
&gt;
&gt; - g-recaptcha-response POST parameter when the user submits the form on your site
&gt; - ...

So I am using [Fetch][3] to create a POST request on the server side to the [verification endpoint][4] with the required body data:

&lt;!-- language: lang-js --&gt;

    verify(req, res, next) {
      const VERIFY_URL = &quot;https://www.google.com/recaptcha/api/siteverify&quot;;

      return fetch(VERIFY_URL, {
        method: &quot;POST&quot;,
        headers: { &quot;Content-Type&quot;: &quot;application/json&quot; },
        body: JSON.stringify({
          secret:   process.env.RECAP_INVIS_SECRET_KEY,
          response: req.body[&#39;g-recaptcha-response&#39;],
        }),
      })
      .then(response =&gt; response.json())
      .then(data =&gt; {
        res.locals.recaptcha = data;
        return next();
      });
    }


But I keep getting the following response:

&gt; {
&gt;  success:        false,
&gt;  error-codes: [ &#39;missing-input-response&#39;, &#39;missing-input-secret&#39; ]
&gt; }

Even though I am passing the response and secret as JSON data in the POST body.

Am I doing something wrong? Regards.

[1]: https://developers.google.com/recaptcha/docs/invisible
[2]: https://developers.google.com/recaptcha/docs/verify
[3]: https://fetch.spec.whatwg.org/
[4]: https://developers.google.com/recaptcha/docs/verify#api-request

reCAPTCHA - error-codes: &#39;missing-input-response&#39;, &#39;missing-input-secret&#39; when verifying user&#39;s response (missing details on POST)

While I was setting up React within Django project I came across this error
   
 ModuleBuildError in 
            Module build failed (from ./node_modules/babel-loader/lib/index.js):
    SyntaxError: C:\Users\1Sun\Cebula3\cebula_react\assets\js\index.js: Support 
    for the experimental syntax &#39;classProperties&#39; isn&#39;t currently enabled (17:9):

      15 | 
      16 | class BodyPartWrapper extends Component {
    &gt; 17 |   state = {
         |         ^
      18 | 
      19 |   }
      20 | 

    Add @babel/plugin-proposal-class-properties (https://git.io/vb4SL) to the 
    &#39;plugins&#39; section of your Babel config to enable transformation.


So, I installed @babel/plugin-proposal-class-properties and put this in babelrc 


**package.json**

  

    {
      &quot;name&quot;: &quot;cebula_react&quot;,
      &quot;version&quot;: &quot;1.0.0&quot;,
      &quot;description&quot;: &quot;&quot;,
      &quot;main&quot;: &quot;index.js&quot;,
      &quot;scripts&quot;: {
        &quot;start&quot;: &quot;webpack-dev-server --config ./webpack.config.js --mode development&quot;,
        &quot;test&quot;: &quot;echo \&quot;Error: no test specified\&quot; &amp;&amp; exit 1&quot;,
        &quot;build&quot;: &quot;webpack --config prod.config.js&quot;
      },
      &quot;keywords&quot;: [],
      &quot;author&quot;: &quot;&quot;,
      &quot;license&quot;: &quot;ISC&quot;,
      &quot;babel&quot;: {
        &quot;presets&quot;: [
          &quot;@babel/preset-env&quot;,
          &quot;@babel/preset-react&quot;
        ]
      },
      &quot;devDependencies&quot;: {
        &quot;@babel/cli&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/core&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/plugin-proposal-class-properties&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/preset-env&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/preset-react&quot;: &quot;^7.0.0&quot;,
        &quot;babel-loader&quot;: &quot;^8.0.2&quot;,
        &quot;babel-plugin-transform-class-properties&quot;: &quot;^6.24.1&quot;,
        &quot;react-hot-loader&quot;: &quot;^4.3.6&quot;,
        &quot;webpack&quot;: &quot;^4.17.2&quot;,
        &quot;webpack-bundle-tracker&quot;: &quot;^0.3.0&quot;,
        &quot;webpack-cli&quot;: &quot;^3.1.0&quot;,
        &quot;webpack-dev-server&quot;: &quot;^3.1.8&quot;
      },
      &quot;dependencies&quot;: {
        &quot;react&quot;: &quot;^16.5.0&quot;,
        &quot;react-dom&quot;: &quot;^16.5.0&quot;
      }
    }


**babelrc**

   

    {
      &quot;presets&quot;: [
        &quot;@babel/preset-env&quot;,
        &quot;@babel/preset-react&quot;
      ],
      &quot;plugins&quot;: [
        &quot;@babel/plugin-proposal-class-properties&quot;
      ]
    }

However the error is still existed, What is the problem??


Support for the experimental syntax &#39;classProperties&#39; isn&#39;t currently enabled

I&#39;m trying to build JS react project with decorators. My .babelrc looks like this:

    {
      &quot;presets&quot;: [
        &quot;@babel/preset-env&quot;,
        &quot;@babel/preset-react&quot;,
    
      ],
      &quot;plugins&quot;: [
        &quot;@babel/plugin-transform-runtime&quot;,
        &quot;@babel/plugin-transform-object-assign&quot;,
        [
          &quot;@babel/plugin-proposal-decorators&quot;,
          {
            &quot;legacy&quot;: true
          }
        ],
        [&quot;@babel/plugin-proposal-class-properties&quot;, { &quot;loose&quot;: true }]
      ]
    }
Adding  @babel/plugin-proposal-decorators problems appears again.


I am using babel 7, webpack 4 and react 16.5

webpack.config.js:

    const path = require(&quot;path&quot;);
    const webpack = require(&quot;webpack&quot;);
    const componentName = &quot;reports-desktop&quot;;
    const publicFolderRelativePath = &quot;../../../../../../public/js&quot;;
    const ignorePlugin = new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/);
    
    module.exports = {
        entry: &#39;./reports-desktop.js&#39;
        ,
        output: {
            path: path.resolve(__dirname, publicFolderRelativePath),
            filename: `${componentName}.js`
        },
        module: {
            rules: [
                {
                    test: /\.js$/,
                    exclude: /node_modules/,
                    use: {
                        loader: &quot;babel-loader&quot;
                    }
                }
            ]
        },
        plugins: [
            ignorePlugin
        ]
    };

package.json: 

    {
      &quot;name&quot;: &quot;captain&quot;,
      &quot;version&quot;: &quot;1.0.0&quot;,
      &quot;description&quot;: &quot;&quot;,
      &quot;main&quot;: &quot;index.js&quot;,
      &quot;scripts&quot;: {
        &quot;watch&quot;: &quot;webpack -w --mode development --progress --color --display-error-details&quot;,
        &quot;build&quot;: &quot;webpack --mode production&quot;
      },
      &quot;keywords&quot;: [],
      &quot;author&quot;: &quot;&quot;,
      &quot;license&quot;: &quot;ISC&quot;,
      &quot;devDependencies&quot;: {
        &quot;@babel/core&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/plugin-proposal-class-properties&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/plugin-proposal-decorators&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/plugin-transform-object-assign&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/plugin-transform-runtime&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/preset-env&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/preset-react&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/preset-stage-1&quot;: &quot;^7.0.0&quot;,
        &quot;@babel/preset-stage-2&quot;: &quot;^7.0.0&quot;,
        &quot;babel-loader&quot;: &quot;^8.0.2&quot;,
        &quot;babel-plugin-transform-decorators&quot;: &quot;^6.24.1&quot;,
        &quot;react&quot;: &quot;^16.5.0&quot;,
        &quot;react-dom&quot;: &quot;^16.5.0&quot;,
        &quot;react-redux&quot;: &quot;^5.0.7&quot;,
        &quot;react-router-dom&quot;: &quot;^4.3.1&quot;,
        &quot;redux&quot;: &quot;^4.0.0&quot;,
        &quot;webpack&quot;: &quot;^4.17.3&quot;,
        &quot;webpack-cli&quot;: &quot;^3.1.0&quot;
      },
      &quot;dependencies&quot;: {
        &quot;axios&quot;: &quot;^0.18.0&quot;,
        &quot;dropzone&quot;: &quot;^5.5.1&quot;,
        &quot;lodash&quot;: &quot;^4.17.10&quot;,
        &quot;moment&quot;: &quot;^2.22.2&quot;,
        &quot;prop-types&quot;: &quot;^15.6.2&quot;,
        &quot;react-addons-update&quot;: &quot;^15.6.2&quot;,
        &quot;react-bootstrap&quot;: &quot;^0.32.4&quot;,
        &quot;react-datetime&quot;: &quot;^2.15.0&quot;,
        &quot;react-dnd&quot;: &quot;^5.0.0&quot;,
        &quot;react-dnd-html5-backend&quot;: &quot;^5.0.1&quot;,
        &quot;react-media&quot;: &quot;^1.8.0&quot;,
        &quot;react-tooltip&quot;: &quot;^3.8.1&quot;
      }
    }

Am I maybe using @babel/plugin-proposal-decorators wrong? As it says in documentation this should fix my problem, but it still appears.


Syntax error - Support for the experimental syntax &#39;decorators-legacy&#39; isn&#39;t currently enabled

I&#39;m working on a web project using Babel 7 with Webpack 4. I&#39;ve never used Babel before and can&#39;t really understand some parts of it. Based on the [documentation][1] I&#39;m using `@babel/preset-env` because it seems the recommended way (especially for beginners). Also using Browserslist integration via my `.browserslistrc` file.

Webpack does the compilation well (`babel-loader` version `8.0.2`), I have no errors but I&#39;m confused about this `useBuiltIns: &quot;entry&quot;` [option mentioned here][2] and how `polyfill` system is working in Babel.  

**.babelrc.js**

    module.exports = {
      presets: [
        [&#39;@babel/preset-env&#39;, {
          &quot;useBuiltIns&quot;: &quot;entry&quot; // do I need this?
        }]
      ],
      plugins: [
        &#39;@babel/plugin-syntax-dynamic-import&#39;
      ]
    };

**.browserslistrc**  
Copied from [here][3] (thought reasonable because my project is using Bootstrap).

    &gt;= 1%
    last 1 major version
    not dead
    Chrome &gt;= 45
    Firefox &gt;= 38
    Edge &gt;= 12
    Explorer &gt;= 10
    iOS &gt;= 9
    Safari &gt;= 9
    Android &gt;= 4.4
    Opera &gt;= 30

**So my questions are:**

1) Do I need to use that `useBuiltIns: &quot;entry&quot;` option?

2) Do I need to install `@babel/polyfill` package and start my `vendors.js` with `require(&quot;@babel/polyfill&quot;);` ?  

3) What if I omit both?

If I do 1 and 2, my `vendors.js` grows up to `411 KB`  
If I ommit both it&#39;s just `341 KB`  
after a production build.

I thought `@babel/preset-env` handles all the rewrites and polyfills by default without any extra `import/require` needed on my side...

Thanks!

**-- EDIT --**

*Babel&#39;s team has just [updated][4] the [docs of `@babel/polyfill`][5] based on some GitHub issues (including mine) complaining about unclear/misleading documentation. Now it&#39;s obvious how to use it. (...and after that my original question seems stupid :)*


  [1]: https://babeljs.io/docs/en/babel-preset-env
  [2]: https://babeljs.io/docs/en/babel-preset-env#browserslist-integration
  [3]: https://github.com/twbs/bootstrap/blob/v4.1.3/.browserslistrc
  [4]: https://github.com/babel/website/pull/1858
  [5]: https://babeljs.io/docs/en/babel-polyfill#usage-in-node-browserify-webpack

Confused about useBuiltIns option of @babel/preset-env (using Browserslist Integration)

Getting same error again again: `Error: Cannot find module &#39;babel-preset-es2015&#39;`.

**Full error log:**
```
ERROR in ./main.js Module build failed (from ./node_modules/babel-loader/lib/index.js): Error: Cannot find module &#39;babel-preset-es2015&#39; from &#39;C:\Users\hp\Desktop\reactApp&#39;
 at Function.module.exports [as sync] (C:\Users\hp\Desktop\reactApp\node_modules\resolve\lib\sync.js:43:15)
 at resolveStandardizedName (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\files\plugins.js:101:31)
 at resolvePreset (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\files\plugins.js:58:10)
 at loadPreset (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\files\plugins.js:77:20)
 at createDescriptor (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\config-descriptors.js:154:9)
 at items.map (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\config-descriptors.js:109:50)
 at Array.map ()
 at createDescriptors (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\config-descriptors.js:109:29)
 at createPresetDescriptors (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\config-descriptors.js:101:10)
 at passPerPreset (C:\Users\hp\Desktop\reactApp\node_modules\@babel\core\lib\config\config-descriptors.js:58:96) @ multi (webpack)-dev-server/client?http://localhost:8080 (webpack)/hot/dev-server.js ./main.js main[2]
```

Cannot find module babel-preset-es2015

What is the difference between
&lt;a href=&quot;https://www.npmjs.com/package/babel-core&quot;&gt;babel-core&lt;/a&gt;  and &lt;a href=&quot;https://www.npmjs.com/package/@babel/core&quot;&gt;@babel/core&lt;/a&gt; ?

Are they the same thing but different versions? If not so, when do you use one and when do you use the other?

Thank you.


Content Type	Original Author	Original Content on Stackoverflow
Question	rap-2-h	View Question on Stackoverflow
Solution 1 - Javascript	connexo	View Answer on Stackoverflow

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