Escaping Strings in JavaScript

Use encodeURI()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURI

Escapes pretty much all problematic characters in strings for proper JSON encoding and transit for use in web applications. It's not a perfect validation solution but it catches the low-hanging fruit.

You can also try this for the double quotes:

JSON.stringify(sDemoString).slice(1, -1);
JSON.stringify('my string with "quotes"').slice(1, -1);

A variation of the function provided by Paolo Bergantino that works directly on String:

String.prototype.addSlashes = function() 
{ 
   //no need to do (str+'') anymore because 'this' can only be a string
   return this.replace(/[\\"']/g, '\\$&').replace(/\u0000/g, '\\0');
} 

By adding the code above in your library you will be able to do:

var test = "hello single ' double \" and slash \\ yippie";
alert(test.addSlashes());

---

EDIT:

Following suggestions in the comments, whoever is concerned about conflicts amongst JavaScript libraries can add the following code:

if(!String.prototype.addSlashes)
{
   String.prototype.addSlashes = function()... 
}
else
   alert("Warning: String.addSlashes has already been declared elsewhere.");

http://locutus.io/php/strings/addslashes/

function addslashes( str ) {
    return (str + '').replace(/[\\"']/g, '\\$&').replace(/\u0000/g, '\\0');
}