QR codes have three parameters: Datatype, size (number of &#39;pixels&#39;) and error correction level. How much information can be stored there also depends on these parameters. For example the lower the error correction level, the more information that can be stored, but the harder the code is to recognize for readers.

The maximum size and the lowest error correction give the following values:  
Numeric only	Max. 7,089 characters  
Alphanumeric	Max. 4,296 characters  
Binary/byte	Max. 2,953 characters (8-bit bytes)

See [this table](http://blog.qr4.nl/page/QR-Code-Data-Capacity.aspx).

A 101x101 QR code, with high level error correction, can hold 3248 bits, or 406 bytes. Probably not enough for any meaningful SVG/XML data.

A 177x177 grid, depending on desired level of error correction, can store between 1273 and 2953 bytes. Maybe enough to store something small.

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/KzV6s.png

I&#39;m trying to use the chrome developer tools to debug an issue I&#39;m having with Twitter oauth.

When the oauth window appears, I open the developer tools to monitor the requests - but as soon as the oauth window closes the developer tools window is also closed. I&#39;d like to be able to keep the developer tools window open so that I can inspect the requests made.

Is this possible?

How do I prevent Chrome developer tools from closing when the current browser window closes?

I realize I watch too many repos in GitHub and the only way I&#39;ve found to unwatch many of them is going to github.com/my_user_name/following, getting inside each of them and pressing Unwatch button.

Isn&#39;t there any way to unwatch them faster and easily?

How to unwatch multiple repos easily on github?

I would like to use this script https://github.com/jeromeetienne/jquery-qrcode&lt;br/&gt;
(or is there even a better solution?)

What I like to do is &quot;save&quot; some small scripts or programs and even files like xml formatted files (svg, x3d, ...) as QR code images.

But how much information (in bytes) can I save exactly to QR code images (using this javascript solution)? 

Any experience with this script and using qr codes for files?&lt;br/&gt;
https://github.com/jeromeetienne/jquery-qrcode

How much data / information can we save / store in a QR code?

I would like to use this script <a href="https://github.com/jeromeetienne/jquery-qrcode<br/" target="_blank" rel="noopener noreferrer">https://github.com/jeromeetienne/jquery-qrcode&#x3C;br/</a>>
(or is there even a better solution?)
What I like to do is "save" some small scripts or programs and even files like xml formatted files (svg, x3d, ...) as QR code images.
But how much information (in bytes) can I save exactly to QR code images (using this javascript solution)?
Any experience with this script and using qr codes for files? 
<a href="https://github.com/jeromeetienne/jquery-qrcode" target="_blank" rel="noopener noreferrer">https://github.com/jeromeetienne/jquery-qrcode</a>

I&#39;m trying to use the HTML5 draggable API (though I realize it [has its problems](http://www.quirksmode.org/blog/archives/2009/09/the_html5_drag.html)). So far, the only showstopper I&#39;ve encountered is that I can&#39;t figure out a way to determine what is being dragged when a `dragover` or `dragenter` event fires:

    el.addEventListener(&#39;dragenter&#39;, function(e) {
      // what is the draggable element?
    });

I realize I could assume that it&#39;s the last element to fire a `dragstart` event, but... multitouch. I&#39;ve also tried using `e.dataTransfer.setData` from the `dragstart` to attach a unique identifier, but apparently that data is [inaccessible](https://developer.mozilla.org/En/DragDrop/DataTransfer#getData()) from `dragover`/`dragenter`:

&gt; This data will only be available once a drop occurs during the drop event.

So, any ideas?

**Update:** As of this writing, HTML5 drag-and-drop does not appear to be implemented in any major mobile browser, making the point about multitouch moot in practice. However, I&#39;d like a solution that&#39;s guaranteed to work across any implementation of [the spec](http://www.whatwg.org/specs/web-apps/current-work/multipage/dnd.html), which does not appear to preclude multiple elements from being dragged simultaneously.

I&#39;ve posted [a working solution](https://stackoverflow.com/a/11089592/66226) below, but it&#39;s an ugly hack. I&#39;m still hoping for a better answer.

Determine what is being dragged from dragenter &amp; dragover events

Pardon the funny title. I&#39;ve created a little graphic demo of 200 balls bouncing and colliding, both against the walls and each other. You can see what I have currently here: http://www.exeneva.com/html5/multipleBallsBouncingAndColliding/

The problem is that whenever they collide with each other, they disappear. I&#39;m not sure why. Can someone take a look and help me out?

UPDATE: Apparently the balls array has balls with coordinates of NaN. Below is the code where I push balls to the array. I&#39;m not entirely sure how the coordinates are getting NaN.

    // Variables
    var numBalls = 200;  // number of balls
    var maxSize = 15;
    var minSize = 5;
    var maxSpeed = maxSize + 5;
    var balls = new Array();
    var tempBall;
    var tempX;
    var tempY;
    var tempSpeed;
    var tempAngle;
    var tempRadius;
    var tempRadians;
    var tempVelocityX;
    var tempVelocityY;
    
    // Find spots to place each ball so none start on top of each other
    for (var i = 0; i &lt; numBalls; i += 1) {
      tempRadius = 5;
      var placeOK = false;
      while (!placeOK) {
        tempX = tempRadius * 3 + (Math.floor(Math.random() * theCanvas.width) - tempRadius * 3);
        tempY = tempRadius * 3 + (Math.floor(Math.random() * theCanvas.height) - tempRadius * 3);
        tempSpeed = 4;
        tempAngle = Math.floor(Math.random() * 360);
        tempRadians = tempAngle * Math.PI/180;
        tempVelocityX = Math.cos(tempRadians) * tempSpeed;
        tempVelocityY = Math.sin(tempRadians) * tempSpeed;
        
        tempBall = {
          x: tempX, 
          y: tempY, 
          nextX: tempX, 
          nextY: tempY, 
          radius: tempRadius, 
          speed: tempSpeed,
          angle: tempAngle,
          velocityX: tempVelocityX,
          velocityY: tempVelocityY,
          mass: tempRadius
        };
        placeOK = canStartHere(tempBall);
      }
      balls.push(tempBall);
    }

Why are my balls disappearing?

How is it possible to make knockout data-bind work on dynamically generated elements? For example, I insert a simple html select menu inside a div and want to populate options using the knockout options binding. This is what my code looks like:

    $(&#39;#menu&#39;).html(&#39;&lt;select name=&quot;list&quot; data-bind=&quot;options: listItems&quot;&gt;&lt;/select&gt;&#39;);

but this method doesn&#39;t work. Any ideas?

knockout data-bind on dynamically generated elements

I need to generate a couple of objects from lists in Javascript. In Python, I&#39;d write this:

    {key_maker(x): val_maker(x) for x in a_list}

Another way to ask is does there exist something like `jQuery.map()` which aggregates objects? Here&#39;s my guess (doesn&#39;t work):

    var result = {}
    $.map(a_list, function(x) {
        $.extend(result, {key_maker(x): val_maker(x)})
    })

In Javascript a dictionary comprehension, or an Object `map`

Can I write the `if else` shorthand without the `else`? 

    var x=1;

    x==2 ? dosomething() : doNothingButContinueCode();   

I&#39;ve noticed putting `null` for the else works (but I have no idea why or if that&#39;s a good idea). 

**Edit:** Some of you seem bemused why I&#39;d bother trying this. Rest assured it&#39;s purely out of curiosity. I like messing around with JavaScript.  

Omitting the second expression when using the if-else shorthand

On my website I would like to display images uploaded by user in a new window with a specific size (`width: 600px`). The problem is that the images may be big. So if they are bigger than these `600px`, I would like to resize them, preserving the aspect ratio.

I tried the `max-width` CSS property, but it doesn&#39;t work: the image&#39;s size doesn&#39;t change. 

Is there any way to solve this problem?

**HTML**:

&lt;!-- language: lang-html --&gt;
          
    &lt;div id=&quot;ImageContainerr&quot;&gt;
        &lt;img src=&quot;DisplayImage.do?ad_id=${requestScope.advert.id}&quot; class=&quot;Image&quot; /&gt;
    &lt;/div&gt;

**CSS**:

&lt;!-- language: lang-css --&gt;

    img.Image { max-width: 100%;}
    div#ImageContainer { width: 600px; }

I also tried setting the `max-width: 600px` for an image, but doesn&#39;t work. The image is streamed from a servlet (it&#39;s stored outside Tomcat&#39;s webapps folder).

How to set max width of an image in CSS

I&#39;m trying to re-size a image in HTML, it&#39;s got width 314px and height 212px. I want to re-size it to 50%... 

but using this I still get a bigger image instead of a half-size image.

    &lt;img src=&quot;image.jpg&quot; width=&quot;50%&quot; height=&quot;50%&quot; /&gt;

What did I do wrong?
Thanks

    &lt;html&gt;
        &lt;head&gt;
        &lt;title&gt;&lt;/title&gt;
        &lt;/head&gt;    
        &lt;body&gt;
        	&lt;div&gt;
        	&lt;img src=&quot;image4.png&quot; width=&quot;50%&quot; height=&quot;50%&quot;/&gt;
            &lt;/div&gt;
        &lt;/body&gt;
    &lt;/html&gt;

I resolved the above problem using jquery below:

    $(document).ready(function(e) {
    		var imgs = document.getElementsByTagName(&#39;img&#39;);
    		var imgLength = imgs.length;
    		
    		for(var i=0; i&lt;= imgLength-1;i++){
    			
    			var imgWidth = imgs[i].clientWidth;
    			var imgHeight = imgs[i].clientHeight;
    		
    			$(&#39;img&#39;).eq(i).attr({width:imgWidth/2, height: imgHeight/2});
    		
    			console.log(imgWidth);
    		}
    		
    		console.log(imgLength);	
        
        });



Image re-size to 50% of original size in HTML

Why am I getting the message &quot;Not a JPEG file: starts with 0x89 0x50&quot; when I try to open my jpg file?


Why am I getting the error: &quot;Not a JPEG file: starts with 0x89 0x50&quot;

If I convert an image (jpg or png) to base64, then will it be bigger, or will it have the same size? How much greater will it be?

Is it recommended to use base64 encoded images on my website?

What is the effect of encoding an image in base64?

So the alert gives undefined values for the width and height. I think the w and h values of the image from the img.onload calculation is not being passed to the values to return, or it may be returning w and h **before** the onload calculates them:

    function getMeta(url){
     var w; var h;
     var img=new Image;
     img.src=url;
     img.onload=function(){w=this.width; h=this.height;};
     return {w:w,h:h}    
    }

    // &quot;http://snook.ca/files/mootools_83_snookca.png&quot; //1024x678
    // &quot;http://shijitht.files.wordpress.com/2010/08/github.png&quot; //128x128
    
    var end = getMeta(&quot;http://shijitht.files.wordpress.com/2010/08/github.png&quot;);
    var w = end.w;
    var h = end.h;
    alert(w+&#39;width&#39;+h+&#39;height&#39;);

How can I have the alert show the correct width and height? 

http://jsfiddle.net/YtqXk/

Get width height of remote image from url

I have two select elements, A and B: when A&#39;s selected option changes, B&#39;s options must be updated accordingly. Each element in A implies many elements in B, it&#39;s a one-to-many relationship (A contains nations, B should contain cities located in the given nation).

The function `do_ajax` should run the asynchronous request:

    function do_ajax(elem, mydata, filename)
    {
        $.ajax({
            url: filename,
            context: elem,
            data: mydata,
            datatype: &quot;html&quot;,
            success: function (data, textStatus, xhr) {
                elem.innerHTML = data;
            }
        });
    }

In order to update B&#39;s options I&#39;ve added a function call in A&#39;s `onChange` event. Here is the function that runs when onChange event (of `A`) is triggered:

    function my_onchange(e) // &quot;e&quot; is element &quot;A&quot;
    {
        var sel_B = ... ; // get select element &quot;B&quot;

        // I skipped some code here
        // ...

        var data = {
            &#39;mode&#39;: &#39;filter_city&#39;,
            &#39;id_A&#39;: e[e.selectedIndex]
        };
        do_ajax(city_sel, data, &#39;ajax_handler.php&#39;);
    }
}


I&#39;ve read in [JQuery docs](http://api.jquery.com/jQuery.ajax/) that `data` can be an array (key value pairs). I get the error if I put:

    var data = {
            &#39;mode&#39;: &#39;filter_city&#39;,
            &#39;id_A&#39;: e[e.selectedIndex]
    };

Instead, I don&#39;t get that error if my data is a string:

    var data = &#39;mode=filter_city&amp;amp;id_A=&#39; + e[e.selectedIndex];

But I need the &quot;array version&quot; of the variable, in my server-side php code. 

The `Uncaught TypeError: Illegal invocation` is located in the &quot;jquery-1.7.2.min.js&quot; file, which is all compressed, so I couldn&#39;t figure out what part of code raised the error.

Is there any setting I can change in my code so that it accepts data as an associative array?

JQuery: &#39;Uncaught TypeError: Illegal invocation&#39; at ajax request - several elements

I send a lot of HTML emails. The problem with GMail is, if there are more than one emails with the same subject, it hides some similar content and shows a &quot;...&quot; to show the &quot;trimmed content&quot;. This screws up with my formatting. 


If changing the subject is not an option, is there is any way to avoid this behaviour?

Edit: I should clarify that I programmatically send emails using Amazon SES from a php script. That is why I posted the question in Stack Overflow. 

How to get rid of &quot;Show trimmed content&quot; in GMail HTML emails?

I have learnt from this [post][1] that always use `&lt;a&gt;` tags or `&lt;button&gt;` tags to make button. Now I&#39;m trying to use `&lt;a&gt;` tag. My question is: is there any way to increase the &lt;a&gt; tag clickable area? Say I&#39;m using `&lt;a&gt;` in a div box. I want the whole div box to become a button. Can I change the &lt;a&gt; clicking area to the whole div box?
Thanks for you help.

  [1]: https://stackoverflow.com/questions/2777256/making-buttons-button-or-div/2777280#comment14500094_2777280

How to increase the clickable area of a &lt;a&gt; tag button?

I was looking for possibility to create QR code reader in my HTML5 based web page. I&#39;ve done some googling and all the links point me to the mobile applications. 

Please help me with some pointers as to how I can use HTML5 and JavaScript to read a QR code containing a url and then redirect the browser to that URL.

How to create a QR code reader in a HTML5 website?

I&#39;ve read that QRCODES has about 4,290 alphanumeric chars limit (about 4kb).

Is it true and is there any way to increase their memory size?

I would like to have more space on if possible: P

QR CODE max char length

&gt; **TL;DR**: I need a way to decode a QR-code from an image file using (preferable pure) Python.

I&#39;ve got a jpg file with a QR-code which I want to decode using Python. I&#39;ve found a couple libraries which claim to do this:

**PyQRCode** ([website here][1]) which supposedly can decode qr codes from images by simply providing a path like this:

    import sys, qrcode
    d = qrcode.Decoder()
    if d.decode(&#39;out.png&#39;):
        print &#39;result: &#39; + d.result
    else:
        print &#39;error: &#39; + d.error

So I simply installed it using `sudo pip install pyqrcode`. The thing I find strange about the example code above however, is that it only imports `qrcode` (and not `pyqrcode` though) Since I think `qrcode` refers to [this library][2] which can only *generate* qr-code images it kind of confused me. So I tried the code above with both `pyqrcode` and `qrcode`, but both fail at the second line saying `AttributeError: &#39;module&#39; object has no attribute &#39;Decoder&#39;`. Furthermore, [the website][1] refers to Ubuntu 8.10 (which came out more than 6 years ago) and I can&#39;t find a public (git or other) repository of it to check the latest commit. So I moved on to the next library:


**ZBar** ([website here][3]) claims to be `&quot;an open source software suite for reading bar codes from various sources, such as image files.&quot;` So I tried installing it on Mac OSX running `sudo pip install zbar`. This fails with `error: command &#39;cc&#39; failed with exit status 1`. I tried to suggestions in the answers to [this SO question][4], but I can&#39;t seem to solve it. So I decided to move on again:

**QRTools**, which according to [this blogpost][5] can decode images easily by using the following code:

    from qrtools import QR
    myCode = QR(filename=u&quot;/home/psutton/Documents/Python/qrcodes/qrcode.png&quot;)
    if myCode.decode():
      print myCode.data
      print myCode.data_type
      print myCode.data_to_string()

So I tried installing it using `sudo pip install qrtools`, which can&#39;t find anything. I also tried it with `python-qrtools`, `qr-tools`, `python-qrtools` and a couple more combinations, but unfortunately to no avail. I suppose it refers to [this repo][6] which says it is based on ZBar (see above). Although I want to run my code on Heroku (and thus prefer a pure Python solution) I successfully installed it on a Linux box (with `sudo apt-get install python-qrtools`) and tried running it:

    from qrtools import QR
    c = QR(filename=&#39;/home/kramer65/qrcode.jpg&#39;)
    c.data  # prints u&#39;NULL&#39;
    c.data_type  # prints u&#39;text&#39;
    c.data_to_string()  # prints &#39;\xef\xbb\xbfNULL&#39; where I expect an int (being `1234567890`)


Although this seems to decode it, It doesn&#39;t seem to do it correctly. It furthermore needs ZBar and is thus not pure Python. So I decided to find yet another library.

**PyXing** ([website here][7]) is supposedly a Python port of the popular Java [ZXing library][8], but the initial and only commit is 6 years old and the project has no readme or documentation whatsoever.

For the rest I found a couple qr-**en**coders (not **de**coders) and some API endpoints which can decode for you. Since I don&#39;t like this service to be dependent on other API endpoints I would want to keep the decoding local though.

So to conclude; would anybody know how I can decode QR-codes from images in (preferable pure) Python? All tips are welcome!


  [1]: http://pyqrcode.sourceforge.net/
  [2]: https://github.com/lincolnloop/python-qrcode
  [3]: http://zbar.sourceforge.net/
  [4]: https://stackoverflow.com/questions/22697440/cc-failed-with-exit-status-1-error-when-install-python-library
  [5]: http://zleap.net/python-qr-code-reader/
  [6]: https://launchpad.net/qr-tools
  [7]: https://github.com/holizz/pyxing
  [8]: https://github.com/zxing/zxing/

How to decode a QR-code image in (preferably pure) Python?

 - I could not find any answers related to the working mechanism of QR code scanning used on [WhatsApp Web][1].
 - **How does the authentication happen when the phone (any smartphone running WhatsApp) scans the QR code on the browser.**
 - I don&#39;t want to know about the technology stack behind them. Like WhatsApp uses modified version of `xmpp`, uses `erlang`, uses web technologies like `socket.io` and `ajax` for the web version to implement such functionality. 
 - The question might be broad. But I am eager to know about the implementation behind it.

  [1]: https://web.whatsapp.com/

Content Type	Original Author	Original Content on Stackoverflow
Question	Daniel Ruf	View Question on Stackoverflow
Solution 1 - Javascript	free_easy	View Answer on Stackoverflow
Solution 2 - Javascript	James	View Answer on Stackoverflow

How much data / information can we save / store in a QR code?

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

Solution 2 - Javascript

How to unwatch multiple repos easily on github?

How do I prevent Chrome developer tools from closing when the current browser window closes?

Attributions