&gt; Executing it in the browser console says SyntaxError: Unexpected token **.

Because that&#39;s the [spec][1]. Designed that way to avoid confusion about whether it&#39;s the square of the negation of one (i.e. `(-1) ** 2`), or the negation of the square of one (i.e. `-(1 ** 2)`). This design was the result of [extensive discussion][2] of operator precedence, and examination of how this is handled in other languages, and finally the decision was made to avoid unexpected behavior by making this a syntax error.


  [1]: https://www.ecma-international.org/ecma-262/7.0/#sec-exp-operator
  [2]: https://esdiscuss.org/topic/exponentiation-operator-precedence

From the [documentation on MDN](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Exponentiation_(**)):

&gt; In JavaScript, it is impossible to write an ambiguous exponentiation expression, i.e. you cannot put a unary operator (`+`/`-`/`~`/`!`/`delete`/`void`/`typeof`) immediately before the base number.

The reason is also explained in that same text:

&gt; In most languages like PHP and Python and others that have an exponentiation operator (typically `^` or `**`), the exponentiation operator is defined to have a higher precedence than unary operators such as unary `+` and unary `-`, but there are a few exceptions. For example, in Bash the `**` operator is defined to have a lower precedence than unary operators. 

So to avoid confusion it was decided that the code must remove the ambiguity and explicitly put the parentheses:

    (-1)**2

or:

    -(1**2) 

As a side note, the *binary* `-` is not treated that way -- having lower precedence -- and so the last expression has the same result as this valid expression:

    0-1**2

### Exponentiation Precedence in Other Programming Languages

As already affirmed in above quote, most programming languages that have an infix exponentiation operator, give a higher precedence to that operator than to the unary minus. 

Here are some other examples of programming languages that give a higher precedence to the unary minus operator:

* [bc](https://www.gnu.org/software/bc/manual/html_mono/bc.html#SEC13)
* [VBScript](https://msdn.microsoft.com/fr-fr/library/6s7zy3d1(v=vs.84).aspx)
* [AppleScript](https://developer.apple.com/library/content/documentation/AppleScript/Conceptual/AppleScriptLangGuide/reference/ASLR_operators.html#//apple_ref/doc/uid/TP40000983-CH5g-SW3)
* [COBOL](https://www.ibm.com/support/knowledgecenter/SS6SG3_4.2.0/com.ibm.entcobol.doc_4.2/PGandLR/tasks/tpari35.htm)
* [Rexx](https://www.ibm.com/support/knowledgecenter/en/SS9UMF_12.1.0/ref/ref/tpc/dsq_rexx_operator.html)
* [Orc](https://orc.csres.utexas.edu/documentation/html/refmanual/ref.syntax.precedence.html)



I&#39;m learning about microservices and I&#39;m gonna build a project with a microservices architecture.

The thing is, one of my team mates want to use one database for all services, sharing all tables so &quot;data doesn&#39;t get repeated&quot;, each service would be built with different frameworks and languages like django and rails which use very different ORM standards.

What would be the correct approach? Since I think working with one database would involve a lot of &quot;hacking&quot; the ORMs in order to make them work correctly.

Microservices with shared database? using multiple ORM&#39;s?

Until now I was using `std::queue` in my project. I measured the average time which a specific operation on this queue requires. 

The times were measured on 2 machines: My local Ubuntu VM and a remote server.
Using `std::queue`, the average was almost the same on both machines: ~750 microseconds. 

Then I &quot;upgraded&quot; the `std::queue` to `boost::lockfree::spsc_queue`, so I could get rid of the mutexes protecting the queue. On my local VM I could see a huge performance gain, the average is now on 200 microseconds. On the remote machine however, the average went up to 800 microseconds, which is slower than it was before. 

First I thought this might be because the remote machine might not support the lock-free implementation:

From the [Boost.Lockfree page:][1]
&gt; Not all hardware supports the same set of atomic instructions. If it is not available in hardware, it can be emulated in software using guards. However this has the obvious drawback of losing the lock-free property.

To find out if these instructions are supported, `boost::lockfree::queue` has a method called `bool is_lock_free(void) const;`. 
However, `boost::lockfree::spsc_queue` does not have a function like this, which, for me, implies that it does not rely on the hardware and that is is always lockfree - on any machine. 

What could be the reason for the performance loss?

---

Exmple code (Producer/Consumer)
==============

    // c++11 compiler and boost library required
    
    #include &lt;iostream&gt;
    #include &lt;cstdlib&gt;
    #include &lt;chrono&gt;
    #include &lt;async&gt;
    #include &lt;thread&gt;
    /* Using blocking queue:
     * #include &lt;mutex&gt;
     * #include &lt;queue&gt;
     */
    #include &lt;boost/lockfree/spsc_queue.hpp&gt;
    
    
    boost::lockfree::spsc_queue&lt;int, boost::lockfree::capacity&lt;1024&gt;&gt; queue;
    
    /* Using blocking queue:
     * std::queue&lt;int&gt; queue;
     * std::mutex mutex;
     */
    
    int main()
    {
    	auto producer = std::async(std::launch::async, [queue /*,mutex*/]() 
    	{
    		// Producing data in a random interval
    		while(true)
    		{
    			/* Using the blocking queue, the mutex must be locked here.
    			 * mutex.lock();
    			 */
    			
    			// Push random int (0-9999)
    			queue.push(std::rand() % 10000);
    
    			/* Using the blocking queue, the mutex must be unlocked here.
    			 * mutex.unlock();
    			 */
    	
    			// Sleep for random duration (0-999 microseconds)
    			std::this_thread::sleep_for(std::chrono::microseconds(rand() % 1000));
    		}
    	}
    
    	auto consumer = std::async(std::launch::async, [queue /*,mutex*/]() 
    	{
    		// Example operation on the queue.
    		// Checks if 1234 was generated by the producer, returns if found.
    
    		while(true)
    		{
    			/* Using the blocking queue, the mutex must be locked here.
    			 * mutex.lock();
    			 */
    
    			int value;
    			while(queue.pop(value)
    			{
    				if(value == 1234)
    					return;
    			}
    
    			/* Using the blocking queue, the mutex must be unlocked here.
    			 * mutex.unlock();
    			 */
    
    			// Sleep for 100 microseconds
    			std::this_thread::sleep_for(std::chrono::microseconds(100));
    		}
    	}
    
    	consumer.get();
    	std::cout &lt;&lt; &quot;1234 was generated!&quot; &lt;&lt; std::endl;
    	return 0;
    }


  [1]: http://www.boost.org/doc/libs/1_59_0/doc/html/lockfree.html

Using Boost.Lockfree queue is slower than using mutexes

Executing it in the browser console it says `SyntaxError: Unexpected token **`.
Trying it in node:

    &gt; -1**2
    ...
    ...
    ...
    ...^C

I thought this is an arithmetic expression where `**` is the power operator. There is no such issue with other operators.

Strangely, typing `*/` on the second line triggers the execution:

    &gt; -1**2
    ... */
    -1**2
      ^^
    SyntaxError: Unexpected token **

What is happening here?

Why is -1**2 a syntax error in JavaScript?

Executing it in the browser console it says <code>SyntaxError: Unexpected token **</code>.
Trying it in node:
<pre><code class="hljs language-python-repl">> -1**2
...
...
...
...^C
</code></pre>
I thought this is an arithmetic expression where <code>**</code> is the power operator. There is no such issue with other operators.
Strangely, typing <code>*/</code> on the second line triggers the execution:
<pre><code class="hljs language-markdown">> -1**2
... */
-1**2
 ^^
SyntaxError: Unexpected token **
</code></pre>
What is happening here?

I have an array of objects containing some information. I am not able to render them in the order I want and I need some help with that. I render them like this:      

    this.state.data.map(
        (item, i) =&gt; &lt;div key={i}&gt; {item.matchID} {item.timeM} {item.description}&lt;/div&gt;
    )

Is it possible to sort them ascending with `item.timeM` in that `map()`-function or do I have to sort them before i use map? 

Sort an array of objects in React and render them

How to force a working print dialog for a multi page (printing the first page is working) PDF in mobile Safari?

Side info:
If I &quot;*long tap*&quot; the PDF in mobile Safari I get a &quot;*Save image as*&quot; dialogue. Maybe the mobile Safari implementation renders the PDF as image and I should search for a solution that this engine renders multiple pages?!

Force print dialog in mobile Safari for multi page PDF

I am experimenting with a more functional style in my JavaScript; therefore, I have replaced for loops with utility functions such as map and reduce.  However, I have not found a functional replacement for while loops since tail call optimization is generally not available for JavaScript.  (From what I understand ES6 prevents tail calls from overflowing the stack but does not optimize their performance.)

I explain what I have tried below, but the TLDR is:
If I don&#39;t have tail call optimization, what is the functional way to implement while loops?

What I have tried:

Creating a &quot;while&quot; utility function:

    function while(func, test, data) {
      const newData = func(data);
      if(test(newData)) {
        return newData;
      } else {
        return while(func, test, newData);
      }
    }

Since tail call optimization isn&#39;t available I could rewrite this as:

    function while(func, test, data) {
      let newData = *copy the data somehow*
      while(test(newData)) {
        newData = func(newData);
      }
      return newData;
    }

However at this point it feels like I have made my code more complicated/confusing for anyone else who uses it, since I have to lug around a custom utility function.  The only practical advantage that I see is that it forces me to make the loop pure; but it seems like it would be more straightforward to just use a regular while loop and make sure that I keep everything pure.

I also tried to figure out a way to create a generator function that mimics the effects of recursion/looping and then iterate over it using a utility function like find or reduce.  However, I haven&#39;t figured out an readable way to do that yet.

Finally, replacing for loops with utility functions makes it more apparent what I am trying to accomplish (e.g. do a thing to each element, check if each element passes a test, etc.).  However, it seems to me that a while loop already expresses what I am trying to accomplish (e.g. iterate until we find a prime number, iterate until the answer is sufficiently optimized, etc.).

So after all this, my overall question is: If I need a while loop, I am programming in a functional style, and I don&#39;t have access to tail call optimization, then what is the best strategy.

How do I replace while loops with a functional programming alternative without tail call optimization?

I build a relay small webpack and typescript demo to play with.
If i run webpack with the webpack.config.js i get this error:

    ERROR in ./js/app.ts
    Module not found: Error: Can&#39;t resolve &#39;./MyModule&#39; in &#39;/Users/timo/Documents/Dev/Web/02_Tests/webpack_test/js&#39;
     @ ./js/app.ts 3:17-38

I have no clue what the problem could be. The module export should be correct.

[Folder Structure][1]

webpack.config.js
&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-js --&gt;

    const path = require(&#39;path&#39;);

    module.exports = {
        entry: &#39;./js/app.ts&#39;,
        output: {
            path: path.resolve(__dirname, &#39;dist&#39;),
            filename: &#39;bundle.js&#39;
        },
        module: {
            rules: [
                {test: /\.ts$/, use: &#39;ts-loader&#39;}
            ]
        }
    };

&lt;!-- end snippet --&gt;

tsconfig.json
&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-js --&gt;

    {
      &quot;compilerOptions&quot;: {
            &quot;target&quot;: &quot;es5&quot;,
            &quot;suppressImplicitAnyIndexErrors&quot;: true,
            &quot;strictNullChecks&quot;: false,
            &quot;lib&quot;: [
                &quot;es5&quot;, &quot;es2015.core&quot;, &quot;dom&quot;
            ],
            &quot;module&quot;: &quot;commonjs&quot;,
            &quot;moduleResolution&quot;: &quot;node&quot;,
            &quot;outDir&quot;: &quot;dist&quot;
        },
        &quot;include&quot;: [
            &quot;js/**/*&quot;
        ]
    }

&lt;!-- end snippet --&gt;

src/app.js
&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-js --&gt;

    import { MyModule } from &#39;./MyModule&#39;;

    let mym = new MyModule();
    console.log(&#39;Demo&#39;);

    mym.createTool();
    console.log(mym.demoTool(3,4));

&lt;!-- end snippet --&gt;

src/MyModule.ts

&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-js --&gt;

    export class MyModule {
       createTool() {
        console.log(&quot;Test 123&quot;);
      }

       demoTool(x:number ,y:number) {
        return x+y;
      }
    };

&lt;!-- end snippet --&gt;

src/index.html

&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-html --&gt;

    &lt;html&gt;
        &lt;head&gt;
            &lt;title&gt;Demo&lt;/title&gt;
            &lt;base href=&quot;/&quot;&gt;
        &lt;/head&gt;
        &lt;body&gt;
            
            &lt;script src=&quot;dist/bundle.js&quot;&gt;&lt;/script&gt;
        &lt;/body&gt;
    &lt;/html&gt;

&lt;!-- end snippet --&gt;


  [1]: https://i.stack.imgur.com/806CP.png

Webpack cant resolve TypeScript modules

I&#39;m trying to show some data using a doughnut chart from Chart.js2.

My current chart looks like this:  
[![current chart][1]][1]

My desired output must show another attribute, which is the percentage, and looks like this:  
[![desired chart with percentage][2]][2]

I&#39;ve read the documentation, but I can&#39;t cope with this because it&#39;s very general and I&#39;m new to JavaScript.

My code for the first chart is the following:

    const renderCashCurrencyPie = (cashAnalysisBalances) =&gt; {
      if (cashAnalysisBalances) {
        const currenciesName = cashAnalysisBalances
        .map(curName =&gt; curName.currency);
    
        const availableCash = cashAnalysisBalances
        .map(avCash =&gt; avCash.availableCash);
    
        let currenciesCounter = 0;
        for (let i = 0; i &lt; currenciesName.length; i += 1) {
          if (currenciesName[i] !== currenciesName[i + 1]) {
            currenciesCounter += 1;
          }
        }
    
        const currenciesData = {
          labels: currenciesName,
          datasets: [{
            data: availableCash,
            backgroundColor: [
              &#39;#129CFF&#39;,
              &#39;#0C6DB3&#39;,
              &#39;#FF6384&#39;,
              &#39;#00FFFF&#39;
            ],
            hoverBackgroundColor: [
              &#39;#FF6384&#39;,
              &#39;#36A2EB&#39;,
              &#39;#FFCE56&#39;,
              &#39;#00FFFF&#39;
            ]
          }]
        };

[1]: https://i.stack.imgur.com/0VHP3.png
[2]: https://i.stack.imgur.com/aM5mq.png

How to customize the tooltip of a Chart.js 2.0 Doughnut Chart?

I was trying to raise an integer to a power using the caret operator (`^`), but I am getting surprising results, e.g.:

    assert_eq!(2^10, 8);

How can I perform exponentiation in Rust?

How to raise a number to a power?

I&#39;ve been testing my React.js application on internet explorer, and finding that some ES6/7 code like `Array.prototype.includes()` breaks it. 

I&#39;m using [create-react-app][1], and apparently they&#39;ve chosen not to include a lot of polyfills since not everyone needs them, and they slow down build times (see for example [here][2] and [here][3]). The documentation (at time of writing) suggests:

&gt; If you use any other ES6+ features that need runtime support (such as
&gt; Array.from() or Symbol), make sure you are including the appropriate
&gt; polyfills manually, or that the browsers you are targeting already
&gt; support them.

So... **what is the best way to &#39;manually&#39; include them?** 

  [1]: https://github.com/facebookincubator/create-react-app
  [2]: https://github.com/facebookincubator/create-react-app/issues/942
  [3]: https://github.com/facebook/create-react-app/issues/914#issuecomment-255336818

Best way to polyfill ES6 features in React app that uses create-react-app

There are already a lot of [cool features][1] in ES6/ES7 for defining Javascript objects. However, the following pattern is common in Javascript:

&lt;!-- language: lang-js --&gt;

    const obj = { 
      requiredKey1: ..., 
      requiredKey2: ... 
    };
    
    if (someCondition) { 
      obj.optionalKey1 = ...;
    }

Is there a way to define the object all at once with both optional and required keys?

  [1]: https://devhints.io/es6

Content Type	Original Author	Original Content on Stackoverflow
Question	psmith	View Question on Stackoverflow
Solution 1 - Javascript	user663031	View Answer on Stackoverflow
Solution 2 - Javascript	trincot	View Answer on Stackoverflow

Why is -1**2 a syntax error in JavaScript?

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

Solution 2 - Javascript

Exponentiation Precedence in Other Programming Languages

Using Boost.Lockfree queue is slower than using mutexes

Microservices with shared database? using multiple ORM's?

Attributions