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Replace line end with line end + double quote javascript

I started something that appeared pretty easy, but it worked out differently.
I have this string, read from a file:
"columns:[
{
allowNull:false,
I want to replace the newline with a newline and a double-quote.
so I do:
text = text.replace(/\r?\n/g, '\n"')
somehow, the output is this:
"columns:[
\"{
\"allowNull:false,
I'm completely puzzled as to where the extra '\' is coming from. If I use a single-quote, or another character, it works just fine
What is going on here?

Within here
text = text.replace(/\r?\n/g, '\n"')
you replace with \n" instead of \n. As #vlaz indicates correctly in the comments, text.replace does not escape " to \". But the print function does.
Anyway, there's a " which may be not intended.

How to make replace() global in JavaScript

I know this question had been asked lot of time but i could not find solution. I have some smilies which each of them has code to be rendered as smiley using replace() , but I get syntax error, I don't know why and how to render my code :/ to smiley
txt = " Hi :/ ";
txt.replace("/\:/\/g","<img src='img/smiley.gif'>");

Your regular expression doesn't need to be in quotes. You should escape the correct / forward slash (you were escaping the wrong slash) and assign the replacement, since .replace doesn't modify the original string.
txt = " Hi :/ ";
txt = txt.replace(/:\//g,"<img src='img/smiley.gif'>");
Based on jonatjano's brilliant deduction, I think you should add a little more to the regular expression to avoid such calamities as interfering with URLs.
txt = txt.replace(/:\/(?!/)/g,"<img src='img/smiley.gif'>");
The above ensures that :// is not matched by doing a negative-lookahead.

There are two problems in the first argument of replace() it escapes the wrong characters and it uses a string that seems to contain a regex instead of a real RegExp.
The second line should read:
txt.replace(/:\//g,"<img src='img/smiley.gif'>");
/:\//g is the regex. The first and the last / are the RegExp delimiters, g is the "global" RegExp option (String.replace() needs a RegExp instead of a string to do a global replace).
The content of the regex is :/ (the string you want to find) but because / has a special meaning in a RegExp (see above), it needs to be escaped and it becomes :\/.

Javascript replacing double backslashed with single backslash

I have been browsing lots of solutions, but somewhy haven't got anything to work.
I need to replace following string: "i:0#.w|dev\\tauri;" with "i:0#.w|dev\tauri;"
I have tried following JS codes to replace:
s.replace(/\\\\/g, "\\$1");
s.replace(/\\\\/g, "\\");
But have had no result. Yet following replaced my \\ with "
s.replace(/\\/g, "\"");
To be honset, then I am really confused behind this logic, it seems like there should be used \\\\ for double backshashed yet it seems to work with just \\ for two backshashes..
I need to do this for comparing if current Sharepoint user (i:0#.w|dev\tauri) is on the list.
Update:
Okay, after I used console.log();, I discovered something interesting.
Incode: var CurrentUser = "i:0#.w|dev\tauri"; and console.log(): i:0#.w|dev auri...
C# code is following:
SPWeb theSite = SPControl.GetContextWeb(Context);
SPUser theUser = theSite.CurrentUser;
return theUser.LoginName;

JavaScript strings need to be escaped so if you are getting a string literal with two back slashes, JavaScript interprets it as just one. In your string you are using to compare, you have \t, which is a tab character, when what you probably want is \\t. My guess is that wherever you are getting the current SharePoint user from, it is being properly escaped, but your compare list isn't.
Edit:
Or maybe the other way around. If you're using .NET 4+ JavaScriptStringEncode might be helpful. If you're still having problems it might help to show us how you are doing the comparison.

carriage return encoding

through queries to a Database I am retrieving such data that I previously inserted through HTML textarea or input. When I get the response from my DB , in a JSON object the text field looks like this :
obj : {
text : [some_text] ↵ [some_text]
}
I tried to replace with this function :
string_convert = function(string){
return string.replace("&#8629",'<br>')
.replace('&crarr','<br>')
.replace('/[\n\r]/g','<br>');
}
I have to show this string in HTML ,but it does not seems to work. I'm using UTF-8
Any advice?

The problem you have is that you have enclosed your regex in quotes. This is incorrect.
.replace('/[\n\r]/g','<br>');
^ ^
remove these two quotes
The quotes are unnecessary because the regex is already delimited by the slashes.
By putting quotes in there, you've actually told it that you want to replace a fixed string rather than a regular expression. The fixed string may look like an expression, but with the quotes, it will just be seen as a plain string.
Remove the quotes and it will be seen as an expression, and it will work just fine.
One other thing, though -- in order to make your regex work perfectly, I'd also suggest modifying it slightly. As it stands, it will just replace all the \n and \r characters with <br>. But in some cases, they may come together as a \r\n pair. This should be a single line break, but your expression will replace it with two <br>s.
You could use an expression like this instead:
/\r\n|\n|\r/g
Hope that helps.

you are missing the ending semicolons ; in your code:
string_convert = function(aString){
return aString.replace("↵",'<br>').replace('↵','<br>');
}
this does not necessary solve your problem, but it could likely.

From: Trying to translate a carriage return into a html tag in Javascript?
text = text.replace(/(\r\n|\n|\r)/g,"<br />");

escape hidden character that is causing JSON validation to fail

I have a hidden character that is causing JSON parsing to fail. What is the best way to escape a string properly just that hidden characters like these done crash my json?
Here is the code, the invisible character is between the n and the s in "brains" until you remove that invisible character JSON.parse() will fail... question is, how to strip the invisible character?
var mystring='{"invis":"their brains process differently"}';
console.log("cool" + mystring);
console.log(JSON.parse(mystring));
Note I found that in the above code actually removed the invisible character, but it is here on pastie, if you want to copy and paste to see the issue:
See the code on pastie

Somehow a cancel character (0x18) got into your string. You can simply replace it out with a regular expression.
var mystring='{"invis":"their brains process differently"}';
mystring = mystring.replace( /\x18/g, "" );
console.log("cool" + mystring);
console.log(JSON.parse(mystring));

I found another JSON parser that doesnt crash with these hidden characters, it is located here:
https://github.com/douglascrockford/JSON-js