We Keep Coding

NodeJS escaping back slash

I am facing some issues with escaping of back slash, below is the code snippet I have tried. Issues is how to assign a variable with escaped slash to another variable.
var s = 'domain\\username';
var options = {
user : ''
};
options.user = s;
console.log(s); // Output : domain\username - CORRECT
console.log(options); // Output : { user: 'domain\\username' } - WRONG
Why when I am printing options object both slashes are coming?
I had feeling that I am doing something really/badly wrong here, which may be basics.
Update:
When I am using this object options the value is passing as it is (with double slashes), and I am using this with my SOAP services, and getting 401 error due to invalid user property value.
But when I tried the same with PHP code using same user value its giving proper response, in PHP also we are escaping the value with two slashes.

When you console.log() an object, it is first converted to string using util.inspect(). util.inspect() formats string property values as literals (much like if you were to JSON.stringify(s)) to more easily/accurately display strings (that may contain control characters such as \n). In doing so, it has to escape certain characters in strings so that they are valid Javascript strings, which is why you see the backslash escaped as it is in your code.

The output is correct.
When you set the variable, the escaped backslash is interpreted into a single codepoint.
However, options is an object which, when logged, appears as a JSON blob. The backslash is re-escaped at this point, as this is the only way the backslash can appear validly as a string value within the JSON output.
If you re-read the JSON output from console.log(options) into javascript (using JSON.parse() or similar) and then output the user key, only one backslash will show.
(Following question edit:)
It is possible that for your data to be accepted by the SOAP consuming service, the data needs to be explicitly escaped in-band. In this case, you will need to double-escape it when assigning the value:
var s = 'domain\\\\user'
To definitively determine whether you need to do this or not, I'd suggest you put a proxy between your working PHP app and the SOAP app, and inspect the traffic.

Regex javascript to only return a value and not full match

How do we do look behind in java script like we can in java or php?
RegEx works for php parser using lookbehind
Here is the working Regex using php parser.
(?<=MakeName=)(.*?)([^\s]+)
This produces the value
(MakeName=)(.*?)([^\s]+)
this produces the match + value
xml response to extract value from.
<ModelName="Tacoma" MakeName="Tundra" Year="2015">
I just need the value

There is no look-behind in JavaScript.
If you are sure the attribute MakeName is present in the input, then you could use this regular expression:
/[^"]*(?!.*\sMakeName\s*=)(?="([^"]*"[^"]*")*[^"]*$)/
It grabs the first series of characters that do not contain a double quote and have a double quote immediately following it, with an even number of double quotes following after that until the end of the input (to make sure we are matching inside a quoted string), but MakeName= should not occur anywhere after the match.
This is of course still not bullet proof, as it will fail for some boundary cases, like with single quoted values.:
<ModelName="Tacoma" MakeName='Tundra' Year="2015">
You could resolve that, if needed, by repeating the same pattern, but then based on single quotes, and combining the two with an OR (|).
Demo:
var s = '<ModelName="Tacoma" MakeName="Tundra" Year="2015">';
result = s.match(/[^"]*(?!.*\sMakeName\s*=)(?="([^"]*"[^"]*")*[^"]*$)/);
console.log(result[0]);

Why doesn't my attempt to escape quotation marks in JSON work?

I am parsing a JSON-string with the JQuery.parseJSON function, as I have done lot's of times in my code. On this particular case, though, I get: Uncaught SyntaxError: Unexpected token R. The only upper case R that exists, in my JSON-formatted String, comes right after an escaped quotation mark, ... \"R ... like this. It seems like too much of a coincidence to be caused by anything other than this, but as far as I can tell, I have completely followed the proper syntax as described on json.org.
EDIT:
I've tried to manually remove the occurrances of \" in a hardcoded test, and the string formats perfectly into a proper Javascript object. In other words, my \" is definitely the problem here...
var myObject = $.parseJSON(myString);
EDIT 2:
the problematic area of my String is here displayed, both in working, and not working condition. first the problematic one:
{"lineID":33,"boxID":10,"title":"My text with the \"Ruining Part\""}
Then the working one:
{"lineID":33,"boxID":10,"title":"My text with the Ruining Part"}
Finally how i format my javabean object into JSON string.
String jsonObjectAsString = new Gson().toJson(myJavaBeanObject);

You probably need to escape the backslash in your string, if it is hardcoded, so that the final string that gets parsed has a single backslash followed by a double quote. Otherwise, the browser thinks you are trying to escape a double quote in your string, which does nothing.
So change your string to:
...\\"R...

Too many quotes within quotes -- what to do?

Here is a section of code used by CKEditor on my website:
CKEDITOR.config.IPS_BBCODE = {"acronym":{"id":"8","title":"Acronym","desc":"Allows you to make an acronym that will display a description when moused over","tag":"acronym","useoption":"1","example":"[acronym='Laugh Out Loud']lol[/acronym]", ...
If you scroll to the right just a little, you will see this:
"[acronym='Laugh Out Loud']lol[/acronym]"
I need to store all of the CKEditor code inside a javascript string, but I can't figure out how to do it because the string has both " and ' in it. See the problem? Furthermore, I don't think I can just escape the quotes because I tried doing that and the editor didn't work.
Any idea what I can do?

You might try taking the string and injecting JavaScript escape codes into it. JavaScript can essentially use any unicode value when using the format: \u#### - so, for a ' character, the code is \u0039, and for the " character, the code is \u0034.
So - you could encode your example portion of the string as:
\u0034[acronym=\u0039Laugh Out Loud\u0039]lol[/acronym]\u0034
Alternatively, you could attempt to simply escape the quotes as in:
\"[acronym=\'Laugh Out Loud\']lol[/acronym]\"
The problem here occurs when you wind up with this kind of situation:
"data:{'prop1':'back\\slash'}"
Which, when escaped in this manner, becomes:
"data:{\'prop\':\'back\\\\slash\'}\"
While this is somewhat more readable than the first version - de-serializing it can be a little tricky when going across object-spaces, such as a javascript object being passed to a C# parser which needs to deserialize into objects, then re-serialize and come back down. Both languages use \ as their escape character, and it is possible to get funky scenarios which are brain-teasers to solve.
The advantage of the \u#### method is that only JavaScript generally uses it in a typical stack - so it is pretty easy to understand what part should be unescaped by what application piece.

hmm.. you said you already tried to escape the quotes and it gave problems.
This shouldn't give problems at all, so try this:
$newstring = addslashes($oldstring);

There's no need to use Unicode escape sequences. Just surround your string with double quotes, and put a backslash before any double quotes within the string.
var x = "\"[acronym='Laugh Out Loud']lol[/acronym]\"";

How to add "\" character in JSON?

I want to add JSON data with the following string value:
json = "d:\xyz\abc";
This value is coming from a database at runtime. When I am going to display it in datatable, JSON formatting error is displayed. My requirement is that the above value will be displayed as it is in the datatable. Please help.

Escape it with another \:
var json = "d:\\xyz\\abc";

You'd better use a JSON library for your programming language. You don't retrieve database values directly with jquery, aren't you?
So, you'd use something like JSON.escape(my_string_from_db), or, in Ruby language I usually do my_string.to_json.
This will automatically escape everything that needs to be escaped.

Change to this:
json = "d:\\xyz\\abc";
See this question for further information

\ is the escape character in JavaScript strings, it gives special meaning to the character following the slash. Like \t is a tab character, \n is a new line. To put a backslash literal you'll need to use \\
The first backslash says the next character is going to be special, the following backslash says "oh, it's just a backslash."