It comes from the English word &#39;let&#39;.

&gt; verb: &quot;let&quot;, &quot;letting&quot;.
1.
to allow or permit:

    // Hey computer, can you please
    let 
    // this
    night = &#39;wonderful&#39;

[Lisp][1] has the keyword `let` and it&#39;s been around since 1958, though it may have come from [even earlier][2].

  [1]: https://en.wikipedia.org/wiki/Lisp_(programming_language)
  [2]: https://en.wikipedia.org/wiki/Let_expression#History

Is it possible to show the [Android Snackbar][1] above the keyboard (as in Y coordinate, not layering)? The Snackbar currently gets hidden if the keyboard is shown, which is an undesirable behavior. 


  [1]: https://developer.android.com/reference/android/support/design/widget/Snackbar.html

Show Android SnackBar above keyboard?

This is my render function:

      render: function() {
        return  &lt;div className=&quot;input-group search-box&quot;&gt;
                  &lt;input
                    onChange={this.handleTextChange}
                    type=&quot;text&quot;
                    value={this.state.text}
                    className=&quot;form-control search-item&quot; /&gt;
                  &lt;span className=&quot;input-group-btn&quot;&gt;&lt;/span&gt;
            &lt;/div&gt;
       }

and I have this as my event handler:

       handleTextChange: function(event) {
         console.log(event.target.value);
         this.setState({
           text: event.target.value
         });
       }

The problem is that when I &quot;save&quot; an item, or console.log print the output, the last character is missing - for instance, if I enter &quot;first&quot;, I&#39;ll get &quot;firs&quot; printed out, and there needs to be another key event to capture the last character. I&#39;ve tried `onKeyUp` - which doesn&#39;t let me type anything in, and I&#39;ve also tried `onKeyDown` and `onKeyPress`, which output nothing. 
What is happening here and why? and how can I get that last character to show up? 

onChange in React doesn&#39;t capture the last character of text

So, I&#39;m a javascript programmer and the new version of [JavaScript (ES6)][1] has a new keyword for declaring variables: `let`, next to the old one `var`. 

I know the difference between these two, but I was asking myself: what does `let` stand for? `var` obviously is an abbreviation of *&quot;**var**iable&quot;*, but `let`? Is it an abbreviation as well? Where does it come from?

I googled this and to my amazement, I couldn&#39;t find an answer. I already knew [Swift][2] also has a `let` keyword (they use it for constants), but apparently some other programming languages use it as well.


  [1]: http://www.ecma-international.org/ecma-262/6.0/index.html
  [2]: https://swift.org/

Linguistic meaning of &#39;let&#39; variable in programming

So, I'm a javascript programmer and the new version of <a href="http://www.ecma-international.org/ecma-262/6.0/index.html" target="_blank" rel="noopener noreferrer">JavaScript (ES6)</a> has a new keyword for declaring variables: <code>let</code>, next to the old one <code>var</code>.
I know the difference between these two, but I was asking myself: what does <code>let</code> stand for? <code>var</code> obviously is an abbreviation of "variable", but <code>let</code>? Is it an abbreviation as well? Where does it come from?
I googled this and to my amazement, I couldn't find an answer. I already knew <a href="https://swift.org/" target="_blank" rel="noopener noreferrer">Swift</a> also has a <code>let</code> keyword (they use it for constants), but apparently some other programming languages use it as well.

I have this Babel loader that&#39;s working

    { test: /\.jsx?$/, loader: &#39;babel&#39;, query: babelSettings, exclude: /node_modules/ },

But now I want a CoffeeScript loader but I want to pipe it through Babel to get the the fancy HMR stuff

    { test: /\.coffee$/, loader: &#39;babel!coffee&#39;, query: babelSettings, exclude: /node_modules/ },

This doesn&#39;t work though, and results in the following error.

&gt; Error: Cannot define &#39;query&#39; and multiple loaders in loaders list

Any idea how to define the query just for the Babel part of the loader chain? The query is a complicated object and I don&#39;t think I can encode it.

    var babelSettings = { stage: 0 };
    
    if (process.env.NODE_ENV !== &#39;production&#39;) {
      babelSettings.plugins = [&#39;react-transform&#39;];
      babelSettings.extra = {
        &#39;react-transform&#39;: {
          transforms: [{
            transform: &#39;react-transform-hmr&#39;,
            imports: [&#39;react&#39;],
            locals: [&#39;module&#39;]
          }, {
            transform: &#39;react-transform-catch-errors&#39;,
            imports: [&#39;react&#39;, &#39;redbox-react&#39;]
          }]
          // redbox-react is breaking the line numbers :-(
          // you might want to disable it
        }
      };
    }



How to add a query to a webpack loader with multiple loaders?

In my component&#39;s render function I have:

    render() {
        const items = [&#39;EN&#39;, &#39;IT&#39;, &#39;FR&#39;, &#39;GR&#39;, &#39;RU&#39;].map((item) =&gt; {
          return (&lt;li onClick={this.onItemClick.bind(this, item)} key={item}&gt;{item}&lt;/li&gt;);
        });
        return (
          &lt;div&gt;
            ...
                    &lt;ul&gt;
                      {items}
                    &lt;/ul&gt;
             ...
          &lt;/div&gt;
        );
      }

everything renders fine, however when clicking the `&lt;li&gt;` element I receive the following error:

&gt; Uncaught Error: Invariant Violation: Objects are not valid as a React
&gt; child (found: object with keys {dispatchConfig, dispatchMarker,
&gt; nativeEvent, target, currentTarget, type, eventPhase, bubbles,
&gt; cancelable, timeStamp, defaultPrevented, isTrusted, view, detail,
&gt; screenX, screenY, clientX, clientY, ctrlKey, shiftKey, altKey,
&gt; metaKey, getModifierState, button, buttons, relatedTarget, pageX,
&gt; pageY, isDefaultPrevented, isPropagationStopped, _dispatchListeners,
&gt; _dispatchIDs}). If you meant to render a collection of children, use an array instead or wrap the object using createFragment(object) from
&gt; the React add-ons. Check the render method of `Welcome`.

If I change to `this.onItemClick.bind(this, item)` to `(e) =&gt; onItemClick(e, item)` inside the map function everything works as expected.

If someone could explain what I am doing wrong and explain why do I get this error, would be great

UPDATE 1:  
onItemClick function is as follows and removing this.setState results in error disappearing.

    onItemClick(e, item) {
        this.setState({
          lang: item,
        });
    }

But I cannot remove this line as I need to update state of this component

Invariant Violation: Objects are not valid as a React child

[`Object.freeze()`][1] seems like a transitional convenience method to move towards using `const` in ES6. 

Are there cases where both take their place in the code or is there a preferred way to work with immutable data?

Should I use [`Object.freeze()`][1] until the moment all browsers I work with support `const` then switch to using `const` instead?


  [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze

Object.freeze() vs const

On our production server, I have minified javascript published and I&#39;m not including a map file with it, because I don&#39;t want the user to be able to understand what&#39;s happening based on the error.  

I have a  logging service I&#39;ve written to forward the angular exceptions (caught by $exceptionHandler) to myself via email.  However, this stack trace is near unreadable:

    n is not defined
        at o (http://localhost:9000/build/app.min.js:1:3284)
        at new NameController (http://localhost:9000/build/app.min.js:1:3412)
        at e (http://localhost:9000/build/bower.min.js:44:193)
        at Object.g.instantiate (http://localhost:9000/build/bower.min.js:44:310)
        at b.$get (http://localhost:9000/build/bower.min.js:85:313)
        at d.compile (http://localhost:9000/build/bower.min.js:321:23333)
        at aa (http://localhost:9000/build/bower.min.js:78:90)
        at K (http://localhost:9000/build/bower.min.js:67:39)
        at g (http://localhost:9000/build/bower.min.js:59:410)
        at http://localhost:9000/build/bower.min.js:58:480 &lt;ui-view class=&quot;ng-scope&quot;&gt;

What I&#39;m wondering is:  Is there a program where I can analyze this stack trace against the actual non-minified source code via map file (or not via map file if there&#39;s another way)



How can I take a minified javascript stack trace and run it against a source map to get the proper error?

I want to show different notification bars for success/error responses,
I pass two callBacks to an redux async action in my react component like this:

    &lt;Button
      onClick={e =&gt; this.props.actions.asyncAction(item, this.showSuccessBar, this.showErrorBar)}
    /&gt;

where asyncAction looks like this: 
   
    export function asyncAction(item, successCallback, errorCallback) {
      return (dispatch, getState) =&gt; {
        dispatch(requestItem(item));
        return fetch(&quot;api.some_url/items/item&quot;)
          .then(response =&gt; response.json())
          .then(json =&gt; {
            if (json.success) {
              dispatch(receivePostsSuccess(reddit, json));
              successCallback();
            } else {
              dispatch(receivePostsFail(reddit, json));
              errorCallback();
            }
          });
        }
      };
    }

Is this considered against the pattern? 
in other words, Should Notification Bars open according to the state change instead of callBacks?

is it considered good practice to pass callBacks to redux async action?

I know this topic is quite popular, but I&#39;m a little iniciate problem in a programming language, the fact is that I still do not understand where I put the code. Well, I&#39;ll tell the whole case:

[![enter image description here][1]][1]

I&#39;m trying to make a modal Swift in a little different from normal: By clicking on a button, the ViewController is displayed (following modal type) on the screen, but with transparent background. Only the blue View with label will be displayed. When this ViewController is presented, it is with transparent background, but as soon as it completes the transition, it will stay with the black background. Already deactivated the opaque option, and tested some options, but nothing this troubleshooting.

Some can help me?

The video is a test in the simulator on the case (https://www.youtube.com/watch?v=wT8Uwmq9yqY).


  [1]: http://i.stack.imgur.com/DGFlN.png

I&#39;m starting with swift, and I&#39;m still pretty lost with how to program in Xcode, I read an answer to a question that has the following code to solve this:

    self.presentingViewController.providesPresentationContextTransitionStyle = YES;
    self.presentingViewController.definesPresentationContext = YES;
    modal.modalPresentationStyle = UIModalPresentationOverCurrentContext;

Where do I put this code?

Swift Modal View Controller with transparent background

Is there an API call within XCTest that I can put into the setUP() or tearDown() to reset the app between tests? I looked in the dot syntax of XCUIApplication and all I saw was the .launch()

OR is there a way to call a shell script in Swift? I could then call xcrun in-between test methods to reset the simulator.

Is there a way to reset the app between tests in Swift XCTest UI?

Why doesn&#39;t this Swift code compile?

    protocol P { }
    struct S: P { }
    
    let arr:[P] = [ S() ]
    
    extension Array where Element : P {
        func test&lt;T&gt;() -&gt; [T] {
            return []
        }
    }
    
    let result : [S] = arr.test()

The compiler says: &quot;Type `P` does not conform to protocol `P`&quot; (or, in later versions of Swift, &quot;Using &#39;P&#39; as a concrete type conforming to protocol &#39;P&#39; is not supported.&quot;).

Why not? This feels like a hole in the language, somehow. I realize that the problem stems from declaring the array `arr` as an array _of a protocol type_, but is that an unreasonable thing to do? I thought protocols were there exactly to help supply structs with something like a type hierarchy?


Protocol doesn&#39;t conform to itself?

while getting cookies from `UIWebView` seems straightforward by using `NSHTTPCookieStorage.sharedHTTPCookieStorage()`, it seems `WKWebView` stores the cookies somewhere else.

I did some research, and I was able to get some cookies from the grabbing it from `NSHTTPURLResponse` object. this, however, does not contain all the cookies used by `WKWebView`:

    func webView(webView: WKWebView, decidePolicyForNavigationResponse navigationResponse: WKNavigationResponse, decisionHandler: (WKNavigationResponsePolicy) -&gt; Void) {
    
      if let httpResponse = navigationResponse.response as? NSHTTPURLResponse {
        if let headers = httpResponse.allHeaderFields as? [String: String], url = httpResponse.URL {
          let cookies = NSHTTPCookie.cookiesWithResponseHeaderFields(headers, forURL: url)
          
          for cookie in cookies {
            logDebug(cookie.description)
            
            logDebug(&quot;found cookie &quot; + cookie.name + &quot; &quot; + cookie.value)
          }
        }
      }
    }


Strangely, there&#39;s also a class `WKWebsiteDataStore` in ios 9 that responsible for managing cookies in `WKWebView`, however, the class does not contain a public method to retrieve the cookies data:

    let storage = WKWebsiteDataStore.defaultDataStore()
      
    storage.fetchDataRecordsOfTypes([WKWebsiteDataTypeCookies], completionHandler: { (records) -&gt; Void in
      for record in records {
        logDebug(&quot;cookie record is &quot; + record.debugDescription)
          
        for dataType in record.dataTypes {
          logDebug(&quot;data type is &quot; + dataType.debugDescription)
            
          // get cookie data??
        }
      }
    })


Is there a workaround for getting the cookie data?

Getting all cookies from WKWebView

I am trying to create an error object to display to the user.

    let userInfo: [NSObject : AnyObject] = 
        [
        &quot;NSLocalizedDescriptionKey&quot; :  NSLocalizedString(&quot;Unauthorized&quot;, comment: &quot;&quot;),
        &quot;NSLocalizedFailureReasonErrorKey&quot; : NSLocalizedString(&quot;Unauthorized&quot;, comment: &quot;&quot;)
        ]
    let err = NSError(domain: &quot;ShiploopHttpResponseErrorDomain&quot;, code: httpResponse.statusCode, userInfo: userInfo)
    print(&quot;Error in Post: \(err.localizedDescription)&quot;)

Unfortunately the output is:
    
    Error in Post: The operation couldn’t be completed.(ShiploopHttpResponseErrorDomain error 401.) 

I want to be able to show to the user that he should activate his account. Any ideas??

Swift creating NSError Object

in es6 there you can define a module of functions like this


    export default {
        foo() { console.log(&#39;foo&#39;) }, 
        bar() { console.log(&#39;bar&#39;) },
        baz() { foo(); bar() }
    }

the above seems to be valid code, but if I call `baz()` it throws an error: 


`ReferenceError: foo is not defined`

How do you call `foo` from another function? in this case `baz`

**Edit**

Here&#39;s the code that actually doesn&#39;t work. I have simplified the code so it&#39;s only the core as needed

    const tokenManager =  {
      revokeToken(headers) { 
        ... 
      },
      expireToken(headers) {
        ...
      },
      verifyToken(req, res, next) {
        jwt.verify(... =&gt; {
          if (err) {
            expireToken(req.headers)
          }
        })
      }
    }
    
    export default tokenManager 

 
and the error is

    expireToken(req.headers);
            ^
    ReferenceError: expireToken is not defined

**Edit 2**

I just tried adding `tokenManager` before `expireToken` and it finally works

ES6 export default with multiple functions referring to each other

I&#39;ve heard that accessing `let` and `const` values before they are initialized can cause a `ReferenceError` because of something called the **temporal dead zone**.

What is the temporal dead zone, how does it relate to scope and hoisting, and in what situations is it encountered?



What is the temporal dead zone?

Is there any way to `map`/`reduce`/`filter`/etc a `Set` in JavaScript or will I have to write my own?

Here&#39;s some sensible `Set.prototype` extensions

    Set.prototype.map = function map(f) {
      var newSet = new Set();
      for (var v of this.values()) newSet.add(f(v));
      return newSet;
    };
    
    Set.prototype.reduce = function(f,initial) {
      var result = initial;
      for (var v of this) result = f(result, v);
      return result;
    };
    
    Set.prototype.filter = function filter(f) {
      var newSet = new Set();
      for (var v of this) if(f(v)) newSet.add(v);
      return newSet;
    };
    
    Set.prototype.every = function every(f) {
      for (var v of this) if (!f(v)) return false;
      return true;
    };
    
    Set.prototype.some = function some(f) {
      for (var v of this) if (f(v)) return true;
      return false;
    };

Let&#39;s take a little set

    let s = new Set([1,2,3,4]);

And some stupid little functions

    const times10 = x =&gt; x * 10;
    const add = (x,y) =&gt; x + y;
    const even = x =&gt; x % 2 === 0;

And see how they work

    s.map(times10);    //=&gt; Set {10,20,30,40}
    s.reduce(add, 0);  //=&gt; 10
    s.filter(even);    //=&gt; Set {2,4}
    s.every(even);     //=&gt; false
    s.some(even);      //=&gt; true

&gt; Isn&#39;t that nice ? Yeah, I think so too. Compare that to the ugly iterator usage

    // puke
    let newSet = new Set();
    for (let v in s) {
      newSet.add(times10(v));
    }

And

    // barf
    let sum = 0;
    for (let v in s) {
      sum = sum + v;
    }

Is there any better way to accomplish `map` and `reduce` using a `Set` in JavaScript?

How to map/reduce/filter a Set in JavaScript?

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?


Content Type	Original Author	Original Content on Stackoverflow
Question	ngstschr	View Question on Stackoverflow
Solution 1 - Javascript	azium	View Answer on Stackoverflow

Linguistic meaning of 'let' variable in programming

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

onChange in React doesn't capture the last character of text

Show Android SnackBar above keyboard?

Attributions