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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]);

adding carriage return don't put the string that follows it at the begining position

I wanted to understand what carriage return is by writint a simple code to console.As carriage return '\r' means
" return to the beginning of the current line without advancing
downward"
But in my code the following string is appended at the end of the line .Why it is behaving like this.I have a string "this is my string" ,then i have carriage return ,and it is followed by another string "that".I thought "that" will be placed at the beginning of the string
console.log("this is my string"+String.fromCharCode(13)+"that");
it prints "this is my stringthat"

Using \r in a string in JavaScript is probably going to give you different results depending on a combination of how the program is being run (in a browser or a standalone engine) and the target of the text (console, alert, a text node in an HTML element etc). It's not clear from your question whether you're running JavaScript in a browser, but (assuming you are) you're going to get different results for different browsers. Internet Explorer's console treats \r as a newline character (\n) while most other browsers will ignore it. I doubt any browser implementation of console is going to give you the behavior you've described.
Note that \r is not a string processing instruction, it's a character. Doing this:
var aString="one\r2";
is never going to result in
aString == "2ne"
or
aString == "2one"
or
aString == "one2"
or anything similar evaluating to true. aString's value will remain "one\r2" until you change it. It's up to the console or alert that is displaying the string to choose how to render \r.
There are string processing methods in JavaScript for splitting and recombining strings (see the w3schools Javascript String Reference or Mozilla's String reference) that would better suit your purposes. If you start using characters like \r or \b in other languages and/or environments you're going to encounter different behaviors based on a whole host of factors.

store arbitrary JavaScript code into a string variable

I have a program (written in Clojure) that injects some JS code into a JS function, then evaluates it via Nashorn. I have no control over the code passes (it may contain quotes, simple quotes...).
It looks like this :
;; Clojure
(eval-str (str "print(evaluateCode(\"" s " \"))"))
// equivalent code in pseudo-js just for those not reading Clojure fluently
evalJS("println(evaluateCode(" + arbitraryJS + "))")
The evaluateCode function is already loaded.
// already loaded in Nashorn
function evaluateCode(code) {
// do something with the code
//...
eval(code);
}
This works fine for simple programs, ex. if arbitraryJS = "var a=123; print(a); return a;".
But as soon as the program contains quotes, it breaks. ex. "var a = 123; print("a is now", a);"
Note : the actual code is there.

You need to escape the string. place a \ before every ".
If you need the \ itself use it double \\
Sorry, I am not allowed to comment yet... :/

I would suggest to escape the quotes and backslashes. I would go for single quotes as JS string delimiters, as in Clojure you are bound to use double quotes for delimiting strings:
;; Clojure
(eval-str (str "print(evaluateCode('"
(clojure.string/replace s #"(['\\\\])" "\\\\$1")
"'))"))
The find and replace patterns each have four backslashes. As in Clojure backslash is an escape character, they actually denote only two backslashes. In regular expressions backslash is also an escape character, so in the end they just denote one, literal backslash each. So this means "prefix any occurrence of backslash or quote with a backslash."
You shouldn't worry about comments and templates and such, as the escape characters only exist in Clojure (after the replace), but are resolved the moment the complete string is parsed by the Javascript engine. The evaluateCode function will never see the escape characters, but the plain value of s.
Example
;; Clojure
(def s "a = 'test'; // 'test' used here")
(eval-str (str "print(evaluateCode('"
(clojure.string/replace s #"(['\\\\])" "\\\\$1")
"'))"))
This will evaluate to:
(eval-str "print(evaluateCode('a = \\'test\\'; // \\'test\\' used here'))")
Note that the backslashes are doubled in the above representation, but that is because Clojure needs that. The actual string only has single occurrences of the backslashes. If instead of calling eval-str, you would call println with the same argument, you would get this output:
print(evaluateCode('a = \'test\'; // \'test\' used here'))
That is the string interpreted by the Javascript engine, and so it interprets the backslashes as escape characters, passing the clean string to evaluateCode.
So if evaluateCode looked like this:
function evaluateCode(code) {
alert(code);
}
It would produce this alert:
a = 'test'; // 'test' used here
So, the escaping backslashes are not there at all in Javascript. It will see the exact same value as the Clojure symbol s represents.

In the after end I used the Apache Commons Lang StringUtils since the other solutions did not work. See it here.

RegExp for remove first and last char and turn ending double slashes into single

I have the following Javascript code to obtain the inner string from an RegExp:
Function.prototype.method = function (name,func){
this.prototype[name] = func;
return this;
};
RegExp.method('toRawString', function(){
return this.toString().replace(/^.(.*).$/,"$1");
});
The purpose of this, is to avoid in string double quoting. For example, if you have a Windows file path "C:\My Documents\My Folder\MyFile.file", you can use it like the following:
alert(/C:\My Documents\My Folder\MyFile.file/.toRawString());
However it is not working for ""C:\My Documents\My Folder\" since it causes syntax error. The only way to avoid it is to keep double quoting at the end of the string. Thus it will be written
alert(/C:\My Documents\My Folder\\/.toRawString());
The fact is any odd number of back slashes on the end of the string will be an error, so all ending back slashes must be double escaped. It will not be hard to use a multiple line small implementation, but are there any single RegExp solution?
NOTE
When using toRawString the RegExp object for this is usually NOT going to be used for any other purpose except for that method. I just want to use the syntax of RegExp to avoid double back slashes in source code. Unfortunately the ending double slashes cannot be easily avoid. I think another workaround is to force a space at the end but that is another question then.
UPDATE
I finally solved the "another question" and posted the code here.

OK, I get what you're trying to do! It's hacky : )
Try something like:
return this.toString().slice(1, -1).replace(/\\+$/, '\\')
Hope that helps.

If you want to include the double quotes in the string just wrap it with single quotes.
s = '"C:\\My Documents\\My Folder\\MyFile.file"'
console.log(s) // Output => "C:\My Documents\My Folder\MyFile.file"

This produces a syntax error:
/C:\My Documents\/
But that regular expression could be written correctly like this:
/C:\\My Documents\\/
Or like this:
new RegExp("C:\\\\My Documents\\\\")
I think your function is just fine and is returning a correct result. Regular expressions just can't end with an unpaired backslash. It's not that you're double escaping - you're just escaping the escape character.
This would produce an error too:
new RegExp("C:\\My Documents\\")
A regular expression like this, for instance, can't be written without a pair of backslashes:
/C:\\What/
Without the second backslash, \W would be interpreted as a special character escape sequence. So escaping the escape character isn't only necessary at the end. It's required anywhere it might be interpreted as the beginning of an escape sequences. For that reason, it might be a good rule of thumb to always use two backslashes to indicate a backslash literal in a regular expression.

Json String with comment out quotes in variable

I have a JSON string hardcoded in my Javascript.
valiJsonString = '{"ssss","ddddddddd\"ddd"}';
The DOM says -> {"ssss","ddddddddd"ddd"}
Can someone tell me why javascript replace my \" into " ?
// try to parse
valiJsonString secureEvalJSON (valiJsonString) //<-- error: jsonString is not valid
working example

"The DOM says" doesn't make much sense, as the DOM doesn't say anything. Do you mean the object browser in Firebug (or some other development console)?
Now, inside a string, \" is the quote character. You have to compensate for this escaping since you do not want it, but instead a verbatim slash.
So perhaps you want \\ followed by ", which is the slashed character followed by the quote character.
In addition, the given JSON looks like it ought to represent an array not an object, since you have no keys:
var str = '["ssss","ddddddddd\\"ddd"]';
The actual value of this JSON-format string inside your browser is now:
["ssss","ddddddddd\"ddd"]

\ is an escape character. try \\

If you want your string to come through escaped, then you need to escape your escape character:
valiJsonString = '{"ssss","ddddddddd\\"ddd"}';

I've added second \ (\ is escape char) and fixed lack of = and type of table {} vs []
http://jsfiddle.net/4wVaR/9/