Yes. `**` is the **exponentiation operator** and is the equivalent of `Math.pow`. 

It was introduced in ECMAScript 2016 (ES7). 

For details, see the [proposal][2] and this [chapter][1] of *Exploring ES2016*. 

  [1]: https://leanpub.com/exploring-es2016-es2017/read#ch_exponentiation-operator
  [2]: https://github.com/rwaldron/exponentiation-operator

`**` was introduced in ECMAScript 2016 (ES7). But keep in mind that not all javascripts environments implements it (for instance, Internet Explorer does not support it).

If you want to be cross browser, you have to use `Math.pow`.

    Math.pow(4, 5)

`**` operator is a valid operator in ES7. It holds the same meaning as `Math.pow(x,y)`
For example, `2**3` is same as `Math.pow(2,3)`

Here are the details from Wikipedia. 

Two new features added in ES7:

&gt; the exponentiation operator (**) and Array.prototype.includes

[https://en.wikipedia.org/wiki/ECMAScript#cite_ref-ES2016_12-1][1]

You can play with this in this [Babel Live compiler][2]


  [1]: https://en.wikipedia.org/wiki/ECMAScript#cite_ref-ES2016_12-1
  [2]: https://babeljs.io/repl/#?babili=false&amp;evaluate=true&amp;lineWrap=false&amp;presets=es2015%2Creact%2Cstage-2&amp;targets=&amp;browsers=&amp;builtIns=false&amp;code=console.log(2**3)%3B

I thought I understood Docker. I understood it as a way to package up software with lots of dependencies..to basically create a little world where absolutely everything is taken care of for a piece of software. Then I stumbled upon this on DockerHub

https://hub.docker.com/_/busybox/

It&#39;s an image for BusyBox, which is a tiny little Linux binary that is meant for embedded systems. Then the top comment says:

&gt; Busybox is awesome :) By far the most useful container per byte on the entire registry.

But I don&#39;t understand at all why this image exists, which makes me think that I don&#39;t actually understand why Docker exists. What is the point of a BusyBox docker image?

I thought I understood Docker until I saw the BusyBox docker image

I want to get the raw http response from my API REST. I have tried with this interface:

    @POST(&quot;/login&quot;)
    @FormUrlEncoded
    Call&lt;retrofit.Response&gt; login(@Field(&quot;username&quot;) String login, @Field(&quot;password&quot;) String pass,
                         @Field(&quot;appName&quot;) String appName, @Field(&quot;appKey&quot;) String appKey);

But I get:

&gt; java.lang.IllegalArgumentException: Unable to create call adapter for
&gt; retrofit.Call&lt;retrofit.Response&gt;
&gt;     for method Api.login

I create `Retrofit` this way:

    Retrofit.Builder retrofitBuilder = new Retrofit.Builder();
    retrofitBuilder.addConverterFactory(JacksonConverterFactory.create());
    Retrofit retrofitAdapter = retrofitBuilder.baseUrl(baseUrl).build();
    return retrofitAdapter.create(apiClass);

Get raw HTTP response with Retrofit

I solved a kata on CodeWars and was looking through some of the other solutions when I came across the double asterisk to signify to the power of. I have done some research and can see that this is a valid operator in python but can see nothing about it in JavaScript documentation.

    var findNb = m =&gt;
    {
      var n = Math.floor((4*m)**.25);
      var sum = x =&gt; (x*(x+1)/2)**2;
      return sum(n) == m ? n : -1;
    }

Yet when I run this solution on CodeWars, it seems to work. I am wondering if this is new in ES6, although I have found nothing about it.

Is the double asterisk ** a valid JavaScript operator?

I solved a kata on CodeWars and was looking through some of the other solutions when I came across the double asterisk to signify to the power of. I have done some research and can see that this is a valid operator in python but can see nothing about it in JavaScript documentation.
<pre><code class="hljs language-ini">var findNb = m =>
{
 var n = Math.floor((4*m)**.25);
 var sum = x => (x*(x+1)/2)**2;
 return sum(n) == m ? n : -1;
}
</code></pre>
Yet when I run this solution on CodeWars, it seems to work. I am wondering if this is new in ES6, although I have found nothing about it.

I am trying to use the new async features and I hope solving my problem will help others in the future. This is my code which is working:

      async function asyncGenerator() {
        // other code
        while (goOn) {
          // other code
          var fileList = await listFiles(nextPageToken);
          var parents = await requestParents(fileList);
          // other code
        }
        // other code
      }
    
      function listFiles(token) {
        return gapi.client.drive.files.list({
          &#39;maxResults&#39;: sizeResults,
          &#39;pageToken&#39;: token,
          &#39;q&#39;: query
        });
      }

The problem is, that my while loop runs too fast and the script sends too many requests per second to the google API. Therefore I would like to build a sleep function which delays the request. Thus I could also use this function to delay other requests. If there is another way to delay the request, please let me know.

Anyway, this is my new code which does not work. The response of the request is returned to the anonymous async function within the setTimeout, but I just do not know how I can return the response to the sleep function resp. to the initial asyncGenerator function.

      async function asyncGenerator() {
        // other code
        while (goOn) {
          // other code
          var fileList = await sleep(listFiles, nextPageToken);
          var parents = await requestParents(fileList);
          // other code
        }
        // other code
      }
    
      function listFiles(token) {
        return gapi.client.drive.files.list({
          &#39;maxResults&#39;: sizeResults,
          &#39;pageToken&#39;: token,
          &#39;q&#39;: query
        });
      }
    
      async function sleep(fn, par) {
        return await setTimeout(async function() {
          await fn(par);
        }, 3000, fn, par);
      }

I have already tried some options: storing the response in a global variable and return it from the sleep function, callback within the anonymous function, etc.

Combination of async function + await + setTimeout

For this code

    var sum = () =&gt; {console.log(arguments); ... }
    sum(2, 3)

Get error `Uncaught ReferenceError: arguments is not defined`.

Why `arguments` is not defined in arrow function?


Why arguments is not defined in arrow function in ES6?

How to convert a date in format `23/10/2015` into a
JavaScript Date format:   

    Fri Oct 23 2015 15:24:53 GMT+0530 (India Standard Time)

How to convert dd/mm/yyyy string into JavaScript Date object?

I&#39;m looking for a way to refactor part of my code to be shorter and simpler, but I don&#39;t know Mongoose very well and I&#39;m not sure how to proceed.

I am trying to check a collection for the existence of a document and, if it doesn&#39;t exist, create it. If it does exist, I need to update it. In either case I need to access the document&#39;s contents afterward.

What I&#39;ve managed to do so far is query the collection for a specific document and, if it&#39;s not found, create a new document. If it is found, I update it (currently using dates as dummy data for this). From there I can access either the found document from my initial `find` operation or the newly saved document and this works, but there must be a better way to accomplish what I&#39;m after.

Here&#39;s my working code, sans distracting extras.

    var query = Model.find({
        /* query */
    }).lean().limit(1);
    
    // Find the document
    query.exec(function(error, result) {
        if (error) { throw error; }
        // If the document doesn&#39;t exist
        if (!result.length) {
            // Create a new one
            var model = new Model(); //use the defaults in the schema
            model.save(function(error) {
                if (error) { throw error; }
                // do something with the document here
            });
        }
        // If the document does exist
        else {
            // Update it
            var query = { /* query */ },
                update = {},
                options = {};
    
            Model.update(query, update, options, function(error) {
                if (error) { throw error; }
                // do the same something with the document here
                // in this case, using result[0] from the topmost query
            });
        }
    });

I&#39;ve looked into `findOneAndUpdate` and other related methods but I&#39;m not sure if they fit my use case or if I understand how to use them correctly. Can anyone point me in the right direction?

(Probably) Related questions:

 - [How to check if that data already exist in the database during update (Mongoose And Express)][1]
 - [Mongoose.js: how to implement create or update?][2]
 - [NodeJS + Mongo: Insert if not exists, otherwise - update][3]
 - [Return updated collection with Mongoose][4]


----------

Edit
----

I didn&#39;t come across the question pointed out to me in my searching, but after reviewing the answers there I&#39;ve come up with this. It&#39;s certainly prettier, in my opinion, and it works, so unless I&#39;m doing something horribly wrong I think my question can probably be closed.

I would appreciate any additional input on my solution.

    // Setup stuff
    var query = { /* query */ },
        update = { expire: new Date() },
        options = { upsert: true };
    
    // Find the document
    Model.findOneAndUpdate(query, update, options, function(error, result) {
        if (!error) {
            // If the document doesn&#39;t exist
            if (!result) {
                // Create it
                result = new Model();
            }
            // Save the document
            result.save(function(error) {
                if (!error) {
                    // Do something with the document
                } else {
                    throw error;
                }
            });
        }
    });

  [1]: https://stackoverflow.com/q/16882938
  [2]: https://stackoverflow.com/q/13337685
  [3]: https://stackoverflow.com/q/13010290
  [4]: https://stackoverflow.com/q/20667739

Mongoose - Create document if not exists, otherwise, update- return document in either case

What is the difference in Typescript between `export` and `default export`. In all the tutorials I see people `export`ing their classes and I cannot compile my code if I don&#39;t add the `default` keyword before exporting.

Also, I couldn&#39;t find any trace of the default export keyword in the official [typescript documentation][1].

    export class MyClass {
    
      collection = [1,2,3];
    
    }

Does not compile. But:

    export default class MyClass {
    
      collection = [1,2,3];
    
    }

Does.

The error is: `error TS1192: Module &#39;&quot;src/app/MyClass&quot;&#39; has no default export.`


  [1]: http://www.typescriptlang.org/

Typescript export vs. default export

numpy has three different functions which seem like they can be used for the same things --- except that `numpy.maximum` can *only* be used element-wise, while `numpy.max` and `numpy.amax` can be used on particular axes, or all elements.  Why is there more than just `numpy.max`?  Is there some subtlety to this in performance?

(Similarly for `min` vs. `amin` vs. `minimum`)

numpy max vs amax vs maximum

If you had a point (in 2d), how could you rotate that point by degrees around the other point (the origin) in python?

You might, for example, tilt the first point around the origin by 10 degrees.

Basically you have one point PointA and origin that it rotates around.
The code could look something like this:

    PointA=(200,300)
    origin=(100,100)

    NewPointA=rotate(origin,PointA,10) #The rotate function rotates it by 10 degrees


Rotate point about another point in degrees python

Background
---------
I am making a function that receives a **positive number** and then rounds the number to the closest integer bellow it.

I have been using [`Math.floor`][1], but recently I discovered [`Math.trunc`][2]. 

I am aware that both will return the same value, given a positive number, and that they work in completely different ways. I am interested in exploring this behavior.

Questions
----------

1. Which one is faster ?
2. Which one should I use?


  [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/floor
  [2]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/trunc

Math.floor VS Math.trunc JavaScript

I&#39;m trying to make `length = 001` in Python 3 but whenever I try to print it out it truncates the value without the leading zeros (`length = 1`). How would I stop this happening without having to cast `length` to a string before printing it out?

How to pad a string with leading zeros in Python 3

`tf.random_normal(shape, mean=0.0, stddev=1.0, dtype=tf.float32, seed=None, name=None)` outputs random values from a normal distribution.

`tf.truncated_normal(shape, mean=0.0, stddev=1.0, dtype=tf.float32, seed=None, name=None)` outputs random values from a truncated normal distribution.

I tried googling &#39;truncated normal distribution&#39;. But didn&#39;t understand much.

What is difference between tf.truncated_normal and tf.random_normal?

When understanding how primitive operators such as `+`, `-`, `*` and `/` are implemented in C, I found the following snippet from [an interesting answer][1].

    // replaces the + operator
    int add(int x, int y) {
        while(x) {
            int t = (x &amp; y) &lt;&lt;1;
            y ^= x;
            x = t;
        }
        return y;
    }

It seems that this function demonstrates how `+` actually works in the background. However, it&#39;s too confusing for me to understand it. I believed that such operations are done using assembly directives generated by the compiler for a long time!

Is the `+` operator implemented as the code posted on **MOST** implementations? Does this take advantage of two&#39;s complement or other implementation-dependent features?

  [1]: https://stackoverflow.com/a/11694778/5399734

Is this how the + operator is implemented in C?

I recently downloaded the **Advanced NSOperations** sample app from Apple and found this code...

    // Operators to use in the switch statement.
    private func ~=(lhs: (String, Int, String?), rhs: (String, Int, String?)) -&gt; Bool {
        return lhs.0 ~= rhs.0 &amp;&amp; lhs.1 ~= rhs.1 &amp;&amp; lhs.2 == rhs.2
    }
    
    private func ~=(lhs: (String, OperationErrorCode, String), rhs: (String, Int, String?)) -&gt; Bool {
        return lhs.0 ~= rhs.0 &amp;&amp; lhs.1.rawValue ~= rhs.1 &amp;&amp; lhs.2 == rhs.2
    }

It seems to use the `~=` operator against `Strings` and `Ints` but I&#39;ve never seen it before.

What is it?

~= operator in Swift

I have an object `X` with a method `getY()` returning an object `Y` with a method `a()`, in typescript.
What does it mean an expression like this one:

    X.getY()!.a()

I guess the `!` operator is used to check against null, but how does it work concretely? Where is defined in the language?

! operator in typescript after object method

Looking at the [list of bitwise operators in the Rust Book][1], I don&#39;t see a NOT operator (like `~` in C).  Is there no NOT operator in Rust?


  [1]: https://doc.rust-lang.org/reference.html#bitwise-operators

What is the bitwise NOT operator in Rust?

While I am installing Magento 2 on my Server, I got an error. After investigating the code and found that there is are three dots (`...`), which is producing the error. I included the code I found below:
```php
return new $type(...array_values($args));
```
What is this operator called, and what is its purpose?

Content Type	Original Author	Original Content on Stackoverflow
Question	Ivan Gonzalez	View Question on Stackoverflow
Solution 1 - Javascript	Tomas Nikodym	View Answer on Stackoverflow
Solution 2 - Javascript	Magus	View Answer on Stackoverflow
Solution 3 - Javascript	Hari Das	View Answer on Stackoverflow

Is the double asterisk ** a valid JavaScript operator?

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

Solution 2 - Javascript

Solution 3 - Javascript

Get raw HTTP response with Retrofit

I thought I understood Docker until I saw the BusyBox docker image

Attributions