Just like you cannot declare a variable with a hyphen, you can&#39;t destructure directly to one. You will need to rename your variable to something else in order to access it on the current scope. You can use the following destructuring syntax to do that:

&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-js --&gt;

    const x = {
      &quot;accept-ranges&quot;:&quot;bytes&quot;,
      &quot;cache-control&quot;:&quot;public, max-age=0&quot;,
      &quot;content-length&quot;:&quot;1174&quot;,
      &quot;content-type&quot;:&quot;application/json&quot;,
      date:&quot;Mon, 03 Oct 2016 06:45:03 GMT&quot;,
      etag:&quot;W/496-157892e555b&quot;,
      &quot;last-modified&quot;:&quot;Mon, 03 Oct 2016 06:14:57 GMT&quot;,
      &quot;x-powered-by&quot;:&quot;Express&quot;
    };
    const { &quot;accept-ranges&quot;: acceptRanges } = x;
    console.log(acceptRanges); // &quot;bytes&quot;

&lt;!-- end snippet --&gt;



I love this Swift syntax; it&#39;s very helpful for many things:

    var foo: Bar = Bar() {
        willSet {
            baz.prepareToDoTheThing()
        }
        didSet {
            baz.doTheThing()
        }
    }

and I&#39;d love to do this in Kotlin. However, [I can&#39;t find the proper syntax](https://www.google.com/search?q=&quot;kotlin&quot;+didSet+willSet)!

**Is there anything in Kotlin like this?**

    var foo: Bar = Bar()
        willSet() {
            baz.prepareToDoTheThing()
        }
        didSet() {
            baz.doTheThing()
        }

Is there a didSet/willSet analog in Kotlin?

I want to build a `HashSet&lt;u8&gt;` from a `Vec&lt;u8&gt;`. I&#39;d like to do this

1. in one line of code,
2. copying the data only once,
3. using only `2n` memory, 

but the only thing I can get to compile is this piece of .. junk, which I think copies the data twice and uses `3n` memory.

    fn vec_to_set(vec: Vec&lt;u8&gt;) -&gt; HashSet&lt;u8&gt; {
        let mut victim = vec.clone();
        let x: HashSet&lt;u8&gt; = victim.drain(..).collect();
        return x;
    }

I was hoping to write something simple, like this:

    fn vec_to_set(vec: Vec&lt;u8&gt;) -&gt; HashSet&lt;u8&gt; {
        return HashSet::from_iter(vec.iter());
    }

but that won&#39;t compile:

&lt;!-- language: none --&gt;

    error[E0308]: mismatched types
     --&gt; &lt;anon&gt;:5:12
      |
    5 |     return HashSet::from_iter(vec.iter());
      |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u8, found &amp;u8
      |
      = note: expected type `std::collections::HashSet&lt;u8&gt;`
      = note:    found type `std::collections::HashSet&lt;&amp;u8, _&gt;`

.. and I don&#39;t really understand the error message, probably because I need to RTFM.

Build HashSet from a vector in Rust

How do I destructure a property from an object where the key contains a hyphen?

Eg:

    {
      accept-ranges:&quot;bytes&quot;,
      cache-control:&quot;public, max-age=0&quot;,
      content-length:&quot;1174&quot;,
      content-type:&quot;application/json&quot;,
      date:&quot;Mon, 03 Oct 2016 06:45:03 GMT&quot;,
      etag:&quot;W/&quot;496-157892e555b&quot;&quot;,
      last-modified:&quot;Mon, 03 Oct 2016 06:14:57 GMT&quot;,
      x-powered-by:&quot;Express&quot;
    }

Now to get the `content-type` and `x-powered-by` values from the object using destructuring?

How to destructure an object with a key containing a hyphen into a variable?

How do I destructure a property from an object where the key contains a hyphen?
Eg:
<pre><code class="hljs language-less">{
 accept-ranges:"bytes",
 cache-control:"public, max-age=0",
 content-length:"1174",
 content-type:"application/json",
 date:"Mon, 03 Oct 2016 06:45:03 GMT",
 etag:"W/"496-157892e555b"",
 last-modified:"Mon, 03 Oct 2016 06:14:57 GMT",
 x-powered-by:"Express"
}
</code></pre>
Now to get the <code>content-type</code> and <code>x-powered-by</code> values from the object using destructuring?

I wanted to add a key:value parameter to all the objects in an array.

eg: 

    var arrOfObj = [{name: &#39;eve&#39;},{name:&#39;john&#39;},{name:&#39;jane&#39;}];

Now I wanted to add a new parameter, isActive to all the objects so the resulting array will look like.

eg: 

        [{
    	name: &#39;eve&#39;,
    	isActive: true
    }, {
    	name: &#39;john&#39;,
    	isActive: true
    }, {
    	name: &#39;jane&#39;,
    	isActive: true
    }]

I can always loop through the array and insert a key,value pair. But was wondering if there was a better way to do so


Add key value pair to all objects in array

`flatMap` is incredibly useful on collections, but javascript does not provide one while having `Array.prototype.map`. Why?

Is there any way to emulate `flatMap` in javascript in both easy and efficient way w/o defining `flatMap` manually?

Why no Array.prototype.flatMap in javascript?

I have a candidate object with properties 

    candidateid:number;
    name:string;

I wish to sort an array of such objects based on the `name` property. How can I achieve this in TypeScript in angular 2?

How to sort object array based on key in typescript

I want to import a CSS file into a react component.

I&#39;ve tried `import disabledLink from &quot;../../../public/styles/disabledLink&quot;;` but I get the error below;

&gt; Module not found: Error: Cannot resolve &#39;file&#39; or &#39;directory&#39; ../../../public/styles/disabledLink in c:\Users\User\Documents\pizza-app\client\src\components @ ./client/src/components/ShoppingCartLink.js 19:20-66 Hash: 2d281bb98fe0a961f7c4 Version: webpack 1.13.2

`C:\Users\User\Documents\pizza-app\client\public\styles\disabledLink.css` is the location of the CSS file I&#39;m trying to load.

To me it seems like import is not looking up the correct path.

I thought with `../../../` it would start to look up the path three folder layers above.

`C:\Users\User\Documents\pizza-app\client\src\components\ShoppingCartLink.js` is the location of the file that should import the CSS file.

What am I doing wrong and how can I fix it?


How to import a CSS file in a React Component

I have the following render method in my React Native code:


&lt;!-- language: lang-js --&gt;

    render() {
        const {height, width} = Dimensions.get(&#39;window&#39;);
        return (
          &lt;View style={styles.container}&gt;
            &lt;Image 
              style={{
                height:height,
                width:width,
              }}
              source={require(&#39;image!foo&#39;)}
              resizeMode=&#39;cover&#39; 
            /&gt;
            &lt;TouchableHighlight style={styles.button}/&gt;
          &lt;/View&gt;
        );
      }


It gives me this error:

&gt; `React.Children.only` expected to receive a single React element child

If I remove the `TouchableHighlight` component, it works fine. If I remove the Image component, it still gives that error.

I can&#39;t see why it gives me this error. `&lt;View&gt;` should be able to have more than one component inside it for rendering.

&quot;React.Children.only expected to receive a single React element child&quot; error when putting &lt;Image&gt; and &lt;TouchableHighlight&gt; in a &lt;View&gt;

Having googled for it I found two solutions:

&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-js --&gt;

        var data = [...Array(10).keys()];
    console.log(data);
        var data1 = Array(8).fill().map((_, i) =&gt; i);
    console.log(data1);


&lt;!-- end snippet --&gt;

data1 displays [0, 1, ..., 7] however data just displays [[object Array Iterator]] how do I actually see the numbers. 

I need it for some iterations over numbers (part of Euler project).

Previously I did a lot of Euler challenges in Python. Now I decided I&#39;ll revisit it and do as much as I can in JS (as much ES6 syntax as possible) to help me develop my js skills.

ES6 - generate an array of numbers

In ES6, is it possible to shorten the following code. I have an `App.js` file and an `index.js`.

**index.js**

    import App from &#39;./App&#39;;

    export default App;

Something like this

**index.js**

    export default App from &#39;./App.js&#39;

Re-export default in ES 6 modules

Consider the following two files:

`app.js`

    import Game       from &#39;./game/game&#39;;
    import React      from &#39;react&#39;;
    import ReactDOM   from &#39;react-dom&#39;;
    
    export default (absPath) =&gt; {
      let gameElement = document.getElementById(&quot;container&quot;);
    
      if (gameElement !== null) {
          ReactDOM.render(
              &lt;Game mainPath={absPath} /&gt;,
              gameElement
          );
      }
    }

`index.js`

    import App from &#39;./src/app&#39;;

The `gulpfile.js`

    var gulp        = require(&#39;gulp&#39;);
    var source      = require(&#39;vinyl-source-stream&#39;);
    var browserify  = require(&#39;browserify&#39;);
    var babelify    = require(&quot;babelify&quot;);
    var watch       = require(&#39;gulp-watch&#39;);
    
    gulp.task(&#39;make:game&#39;, function(){
      return browserify({
        entries: [
          &#39;index.js&#39;
        ]
      })
      .transform(&#39;babelify&#39;)
      .bundle()
      .pipe(source(&#39;index.js&#39;))
      .pipe(gulp.dest(&#39;app/&#39;));
    });

The error:

    gulp make:game
    [13:09:48] Using gulpfile ~/Documents/ice-cream/gulpfile.js
    [13:09:48] Starting &#39;make:game&#39;...
    
    events.js:154
          throw er; // Unhandled &#39;error&#39; event
          ^
    SyntaxError: &#39;import&#39; and &#39;export&#39; may appear only with &#39;sourceType: module&#39;

**What is this error? What am I doing wrong?**

SyntaxError: &#39;import&#39; and &#39;export&#39; may appear only with &#39;sourceType: module&#39; - Gulp

I had a question about why node v6.7 would be failing to run this code:

    var a = {
        foo: &#39;bar&#39;
    }
    
    var b = {
        ...a,
        my: &#39;sharona&#39;
    }
    console.log(b)


Anyone have an idea why that would be? I thought v6 supported object spreading..? But I guess not? Here is the error I&#39;m seeing:

    /home/teselagen/ve/tnrtest.js:6
    	...a,
    	^^^
    SyntaxError: Unexpected token ...
        at Object.exports.runInThisContext (vm.js:76:16)
        at Module._compile (module.js:528:28)
        at Object.Module._extensions..js (module.js:565:10)
        at Module.load (module.js:473:32)
        at tryModuleLoad (module.js:432:12)
        at Function.Module._load (module.js:424:3)
        at Module.runMain (module.js:590:10)
        at run (bootstrap_node.js:394:7)
        at startup (bootstrap_node.js:149:9)
        at bootstrap_node.js:509:3

 

Node v6 failing on object spread

Is there a recommended naming convention for key names within a const object in es6? I haven&#39;t been able to find a resource which states if they should be uppercase or lowercase.


    const COLOR_CODES = {
      BLUE: 1,
      RED: 1
    };
vs

    const COLOR_CODES = {
      blue: 1,
      red: 1
    };

[The examples](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const) from this MDN article show both styles, so maybe both are acceptable.

Naming convention for const object keys in ES6

When I study electron, I found 2 ways of getting BrowserWindow object.

    const {BrowserWindow} = require(&#39;electron&#39;)
and

    const electron = require(&#39;electron&#39;)
    const BrowserWindow = electron.BrowserWindow

What is the difference between `const` and `const {}` in JavaScript?

I can&#39;t understand why the `const {}` can work. Do I miss anything important about JS?


What is the difference between const and const {} in JavaScript

I just came across a question about React performances when settings default values in one of my **stateless functional components**.

This component had a `defaultProps` which defined `row: false`, but I didn&#39;t like it because the `defaultProps` is **at the end** of the file, which actually makes it harder to see. And thus, we aren&#39;t aware of the default property. So I moved it to the function declaration directly and assigned it using ES6 default value for parameters.

    const FormField = ({
      row = false,
      ...others,
    }) =&gt; {
      // logic...
    };

But then we argued with a coworker about this **being a good idea or not**. Because doing so may seem trivial, but may also have a great impact upon performances since **react is not aware** of the default value. 

I believe in this case, it&#39;s trivial. Because it&#39;s a boolean and not an object/array and therefore won&#39;t be seen as a different value during *reconciliation*. 

---

But, let&#39;s now see a more advanced use-case:

    const FormField = ({
      input: { name, value, ...inputRest },
      label = capitalize(name),
      placeholder = label,
      row = false,
      meta: { touched, error, warning },
      ...others,
    }) =&gt; {
      // logic...
    };

Here, I base the value of `placeholder` from `label`, which itself is based on `input.name`. Using ES6 destructuring with default values for parameters makes the whole thing quite easy to write/understand and it works like a charm.

But is it a good idea? And if not, then how would you do it properly?

React - defaultProps vs ES6 default params when destructuring (performances issues)

I have a sort filter that takes an array to populate the options. Trying to see the option `value` equal to the text within the array but I get the error within the title: 

    Invalid attempt to destructure non-iterable instance


I need to pass the text as the value within the option tag so that when the user updates the filter, the correct text displays to the choice the user made.

Here is my code: 

    function Sorting({by, order, rp}: SortingProps) {
    	const opts = [
    		[&#39;Price (low)&#39;, &#39;price&#39;, &#39;asc&#39;],
    		[&#39;Price (high)&#39;, &#39;price&#39;, &#39;desc&#39;],
    		[&#39;Discount (low)&#39;, &#39;discount&#39;, &#39;asc&#39;],
    		[&#39;Discount (high)&#39;, &#39;discount&#39;, &#39;desc&#39;],
    		[&#39;Most popular&#39;, &#39;arrival&#39;, &#39;latest&#39;],
    		[&#39;Most recent&#39;, &#39;arrival&#39;, &#39;latest&#39;],
    	];
    
    	const onChange = (i) =&gt; {
    		const [text, by, order] = opts[i];
    		refresh({so: {[by]: order}});
    		/* GA TRACKING */
    		ga(&#39;send&#39;, &#39;event&#39;, &#39;My Shop Sort By&#39;, text, &#39;Used&#39;);
    	};
        
        return (
            &lt;div className={cn(shop.sorting, rp.sorting.fill &amp;&amp; shop.sortingFill)}&gt;
                &lt;Select className={shop.sortingSelect} label=&quot;Sort By&quot; onChange={onChange} value={`${by}:${order}`}&gt;
                    {opts.map(([text], i) =&gt;
                        &lt;Option key={i} value={text}&gt;{text}&lt;/Option&gt;
                    )}
                &lt;/Select&gt;
            &lt;/div&gt;
        )
    }



React JS Error: Invalid attempt to destructure non-iterable instance

Can I avoid declaring a useless variable when array destructuring when I am only interested in array values beyond index 0?

In the following, I want to avoid declaring `a`, I am only interested in index 1 and beyond.

&lt;!-- begin snippet: js hide: false console: true babel: true --&gt;

&lt;!-- language: lang-js --&gt;

    // How can I avoid declaring &quot;a&quot;?
    const [a, b, ...rest] = [1, 2, 3, 4, 5];

    console.log(a, b, rest);

&lt;!-- end snippet --&gt;



How can I ignore certain returned values from array destructuring?

In JavaScript ES6, you are able to destructure arrays like this:

    const [a,b,...rest] = someArray;

where `a` is the first element in the array, `b` is the second, and `rest` is an array with the remaining elements.

I know in C#7 that you can destructure tuples during assignment, but could not find anything related to destructuring arrays/enumerables like this:

    var (a,b) = someTuple;

I have an `IEnumerable` where I need the first and second elements as variables, and I need the rest of the elements as another IEnumerable. I have a solution, but feel that destructuring will look cleaner.


Content Type	Original Author	Original Content on Stackoverflow
Question	Sathish	View Question on Stackoverflow
Solution 1 - Javascript	CodingIntrigue	View Answer on Stackoverflow

How to destructure an object with a key containing a hyphen into a variable?

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

Build HashSet from a vector in Rust

Is there a didSet/willSet analog in Kotlin?

Attributions