&lt;!-- language: lang-js --&gt;

    [1,2,3,4,5,6][1,2,3];
          ^         ^
          |         |
        array       + — array subscript access operation,
                        where index is `1,2,3`,
                        which is an expression that evaluates to `3`.

The second `[...]` cannot be an array, so it’s an array subscript operation. And the contents of a subscript operation are not a delimited list of operands, but a single expression.

Read more about the comma operator [here][1].


  [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comma_Operator

Because `(1,2) == 2`.  You&#39;ve stumbled across the [comma operator](https://tc39.es/ecma262/#sec-comma-operator) (or [simpler explanation here][1]).

Unless commas appear in a declaration list, parameter list, object or array literal, they act like any other binary operator.  `x, y` evaluates `x`, then evaluates `y` and yields that as the result.


  [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comma_Operator

    [1,2,3,4,5,6][1,2,3];

Here the second box i.e. `[1,2,3]` becomes `[3]` i.e. the last item so the result will be 4
for example if you keep `[1,2,3,4,5,6]` in an array 

    var arr=[1,2,3,4,5,6];

    arr[3]; // as [1,2,3] in the place of index is equal to [3]

similarly 

    *var arr2=[1,2,3,4,5,6];

     // arr[1,2] or arr[2] will give 3*

But when you place a + operator in between then the second square bracket is not for mentioning index. It is rather another array
That&#39;s why you get

    [1,2,3] + [1,2] = 1,2,31,2

i.e. 

    var arr_1=[1,2,3];

    var arr_2=[1,2];

    arr_1 + arr_2; // i.e.  1,2,31,2

Basically in the first case it is used as index of array and in the second case it is itself an array.





I know `../` means go up a path, but what does `./` mean exactly?

I was recently going through a tutorial and it seems to be referring to just a file in the same location, so is it necessary at all? Can I just not use it if that&#39;s all it&#39;s doing?

What does &quot;./&quot; (dot slash) refer to in terms of an HTML file path location?

I made a basic rails app with a simple pages controller with an index function and when I load the page I get:


    ActionView::Template::Error (application.css isn&#39;t precompiled):
        2: &lt;html&gt;
        3: &lt;head&gt;
        4:   &lt;title&gt;Demo&lt;/title&gt;
        5:   &lt;%= stylesheet_link_tag    &quot;application&quot; %&gt;
        6:   &lt;%= javascript_include_tag &quot;application&quot; %&gt;
        7:   &lt;%= csrf_meta_tags %&gt;
        8: &lt;/head&gt;
      app/views/layouts/application.html.erb:5:in `_app_views_layouts_application_html_erb__43625033_88530400&#39;


Gemfile

    source &#39;http://rubygems.org&#39;
    
    gem &#39;rails&#39;, &#39;3.1.0&#39;
    
    # Bundle edge Rails instead:
    # gem &#39;rails&#39;,     :git =&gt; &#39;git://github.com/rails/rails.git&#39;
    
    gem &#39;sqlite3&#39;
    
    gem &#39;execjs&#39;
    gem &#39;therubyracer&#39;
    
    # Gems used only for assets and not required
    # in production environments by default.
    group :assets do
      gem &#39;sass-rails&#39;, &quot;  ~&gt; 3.1.0&quot;
      gem &#39;coffee-rails&#39;, &quot;~&gt; 3.1.0&quot;
      gem &#39;uglifier&#39;
    end
    
    gem &#39;jquery-rails&#39;
    
    # Use unicorn as the web server
    # gem &#39;unicorn&#39;
    
    # Deploy with Capistrano
    # gem &#39;capistrano&#39;
    
    # To use debugger
    # gem &#39;ruby-debug19&#39;, :require =&gt; &#39;ruby-debug&#39;
    
    group :test do
      # Pretty printed test output
      gem &#39;turn&#39;, :require =&gt; false
    end



rails 3.1.0 ActionView::Template::Error (application.css isn&#39;t precompiled)

I can&#39;t wrap my mind around this quirk.

    [1,2,3,4,5,6][1,2,3]; // 4
    [1,2,3,4,5,6][1,2]; // 3

I know `[1,2,3] + [1,2] = &quot;1,2,31,2&quot;`, but I can&#39;t find what type or operation is being performed.


Why does [5,6,8,7][1,2] = 8 in JavaScript?

I can't wrap my mind around this quirk.
<pre><code class="hljs language-ini">[1,2,3,4,5,6][1,2,3]; // 4
[1,2,3,4,5,6][1,2]; // 3
</code></pre>
I know <code>[1,2,3] + [1,2] = "1,2,31,2"</code>, but I can't find what type or operation is being performed.

How do you convert an array of characters to a string in JavaScript?

    var s = [&#39;H&#39;, &#39;e&#39;, &#39;l&#39;, &#39;l&#39;, &#39;o&#39;];
    // How to convert s to a string?

Convert a Char Array to a String

My csv data looks like this: 

&gt; heading1,heading2,heading3,heading4,heading5,value1_1,value2_1,value3_1,value4_1,value5_1,value1_2,value2_2,value3_2,value4_2,value5_2....

How do you read this data and convert to an array like this using Javascript?: 

&gt; [heading1:value1_1 , heading2:value2_1, heading3 : value3_1, heading4
&gt; : value4_1, heading5 : value5_1 ],[heading1:value1_2 ,
&gt; heading2:value2_2, heading3 : value3_2, heading4 : value4_2, heading5
&gt; : value5_2 ]....

I&#39;ve tried this code but no luck!:

    &lt;script type=&quot;text/javascript&quot;&gt;
        var allText =[];
        var allTextLines = [];
        var Lines = [];
    
        var txtFile = new XMLHttpRequest();
        txtFile.open(&quot;GET&quot;, &quot;file://d:/data.txt&quot;, true);
        txtFile.onreadystatechange = function()
        {
            allText = txtFile.responseText;
            allTextLines = allText.split(/\r\n|\n/);
        };
    
        document.write(allTextLines);&lt;br&gt;
        document.write(allText);&lt;br&gt;
        document.write(txtFile);&lt;br&gt;
    &lt;/script&gt;

How to read data From *.CSV file using javascript?

Trying to use fileReader.readAsBinaryString to upload a PNG file to the server via AJAX, stripped down code (fileObject is the object containing info on my file);

    var fileReader = new FileReader();
    
    fileReader.onload = function(e) {
        var xmlHttpRequest = new XMLHttpRequest();
        //Some AJAX-y stuff - callbacks, handlers etc.
        xmlHttpRequest.open(&quot;POST&quot;, &#39;/pushfile&#39;, true);
        var dashes = &#39;--&#39;;
    	var boundary = &#39;aperturephotoupload&#39;;
    	var crlf = &quot;\r\n&quot;;
    	
    	//Post with the correct MIME type (If the OS can identify one)
    	if ( fileObject.type == &#39;&#39; ){
            filetype = &#39;application/octet-stream&#39;;
    	} else {
            filetype = fileObject.type;
    	}
    	
    	//Build a HTTP request to post the file
        var data = dashes + boundary + crlf + &quot;Content-Disposition: form-data;&quot; + &quot;name=\&quot;file\&quot;;&quot; + &quot;filename=\&quot;&quot; + unescape(encodeURIComponent(fileObject.name)) + &quot;\&quot;&quot; + crlf + &quot;Content-Type: &quot; + filetype + crlf + crlf + e.target.result + crlf + dashes + boundary + dashes;
    	
        xmlHttpRequest.setRequestHeader(&quot;Content-Type&quot;, &quot;multipart/form-data;boundary=&quot; + boundary);
        
        //Send the binary data
        xmlHttpRequest.send(data);
    }
    
    fileReader.readAsBinaryString(fileObject);


Examining the first few lines of a file before upload (using VI) gives me

![enter image description here][1]

The same file after upload shows

![enter image description here][2]

So it looks like a formatting/encoding issue somewhere, I tried using a simple UTF8 encode function on the raw binary data

    	function utf8encode(string) {
    		string = string.replace(/\r\n/g,&quot;\n&quot;);
    		var utftext = &quot;&quot;;
     
    		for (var n = 0; n &lt; string.length; n++) {
     
    			var c = string.charCodeAt(n);
     
    			if (c &lt; 128) {
    				utftext += String.fromCharCode(c);
    			}
    			else if((c &gt; 127) &amp;&amp; (c &lt; 2048)) {
    				utftext += String.fromCharCode((c &gt;&gt; 6) | 192);
    				utftext += String.fromCharCode((c &amp; 63) | 128);
    			}
    			else {
    				utftext += String.fromCharCode((c &gt;&gt; 12) | 224);
    				utftext += String.fromCharCode(((c &gt;&gt; 6) &amp; 63) | 128);
    				utftext += String.fromCharCode((c &amp; 63) | 128);
    			}
     
    		}
     
    		return utftext;
        )

Then in the original code

    //Build a HTTP request to post the file
    var data = dashes + boundary + crlf + &quot;Content-Disposition: form-data;&quot; + &quot;name=\&quot;file\&quot;;&quot; + &quot;filename=\&quot;&quot; + unescape(encodeURIComponent(file.file.name)) + &quot;\&quot;&quot; + crlf + &quot;Content-Type: &quot; + filetype + crlf + crlf + utf8encode(e.target.result) + crlf + dashes + boundary + dashes;

which gives me the output of

![enter image description here][3]

Still not what the raw file was =(

How do I encode/load/process the file to avoid the encoding issues, so the file being received in the HTTP request is the same as the file before it was uploaded.

Some other possibly useful information, if instead of using fileReader.readAsBinaryString() I use fileObject.getAsBinary() to get the binary data, it works fine. But getAsBinary only works in Firefox. I&#39;ve been testing this in Firefox and Chrome, both on Mac, getting the same result in both. The backend uploads are being handled by the [NGINX Upload Module][4], again running on Mac. The server and client are on the same machine. The same thing is happening with any file I try to upload, I just chose PNG because it was the most obvious example.


  [1]: http://i.stack.imgur.com/cSULu.png
  [2]: http://i.stack.imgur.com/lPjoG.png
  [3]: http://i.stack.imgur.com/J5pva.png
  [4]: http://www.grid.net.ru/nginx/upload.en.html

fileReader.readAsBinaryString to upload files

An input element contains numbers a where comma or dot is used as decimal separator and space may be used to group thousands like this:

&gt; &#39;1,2&#39;  
&gt; &#39;110 000,23&#39;  
&gt; &#39;100 1.23&#39;

How would one convert them to a float number in the browser using JavaScript?

jQuery and jQuery UI are used. `Number(string)` returns *NaN* and `parseFloat()` stops on first space or comma.

Convert String with Dot or Comma as decimal separator to number in JavaScript

I want a function of my choosing to run when a DOM element is added to the page. This is in the context of a browser extension, so the webpage runs independently of me and I cannot modify its source. What are my options here?

I guess that, in theory, I could just use `setInterval()` to continually search for the element&#39;s presence and perform my action if the element is there, but I need a better approach.

Content Type	Original Author	Original Content on Stackoverflow
Question	Joe	View Question on Stackoverflow
Solution 1 - Javascript	Lightness Races in Orbit	View Answer on Stackoverflow
Solution 2 - Javascript	Mike Samuel	View Answer on Stackoverflow
Solution 3 - Javascript	Imdad	View Answer on Stackoverflow

Why does [5,6,8,7][1,2] = 8 in JavaScript?

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

Solution 2 - Javascript

Solution 3 - Javascript

rails 3.1.0 ActionView::Template::Error (application.css isn't precompiled)

What does "./" (dot slash) refer to in terms of an HTML file path location?

Attributions