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Whats wrong with this regex logic

I am trying to fetch the value after equal sign, its works but i am getting duplicated values , any idea whats wrong here?
// Regex for finding a word after "=" sign
var myregexpNew = /=(\S*)/g;
// Regex for finding a word before "=" sign
var mytype = /(\S*)=/g;
//Setting data from Grid Column
var strNew = "QCById=20";
var matchNew = myregexpNew.exec(strNew);
var newtype = mytype.exec(strNew);
alert(matchNew);
https://jsfiddle.net/6vjjv0hv/

exec returns an array, the first element is the global match, the following ones are the submatches, that's why you get ["=20", "20"] (using console.log here instead of alert would make it clearer what you get).
When looking for submatches and using exec, you're usually interested in the elements starting at index 1.
Regarding the whole parsing, it's obvious there are better solution, like using only one regex with two submatches, but it depends on the real goal.

You can try without using Regex like this:
var val = 'QCById=20';
var myString = val.substr(val.indexOf("=") + 1);
alert(myString);
Presently exec is returning you the matched value.

REGEXP.exec(SOMETHING) returns an array (see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/exec).
The first item in the array is the full match and the rest matches the parenthesized substrings.

You do not get duplicated values, you just get an array of a matched value and the captured text #1.
See RegExp#exec() help:
If the match succeeds, the exec() method returns an array and updates properties of the regular expression object. The returned array has the matched text as the first item, and then one item for each capturing parenthesis that matched containing the text that was captured.
Just use the [1] index to get the captured text only.
var myregexpNew = /=(\S*)/g;
var strNew = "QCById=20";
var matchNew = myregexpNew.exec(strNew);
if (matchNew) {
console.log(matchNew[1]);
}
To get values on both sides of =, you can use /(\S*)=(\S*)/g regex:
var myregexpNew = /(\S*)=(\S*)/g;
var strNew = "QCById=20";
var matchNew = myregexpNew.exec(strNew);
if (matchNew) {
console.log(matchNew[1]);
console.log(matchNew[2]);
}
Also, you may want to add a check to see if the captured values are not undefined/empty since \S* may capture an empty string. OR use /(\S+)=(\S+)/g regex that requires at least one non-whitespace character to appear before and after the = sign.

Cut out, and replace a part of a string

There is a part in my string from, to which I would like to replace to an another string replace_string. My code should work, but what if there is an another part like the returned substring?
var from=10, to=17;
//...
str = str.replace(str.substring(from, to), replace_string);
For example:
from=4,to=6
str = "abceabxy"
replace_string = "zz"
the str should be "abcezzxy"

What you want to do is simple! Cut out and replace the string. Here is the basic tool, you need scissor and glue! Oops I mean string.Split() and string.Replace().
How to use?
Well I am not sure if you want to use string.Split() but you have used string.Replace() so here goes.
String.Replace uses two parameters, like this ("one", "two") what you need to make sure is that you are not replacing a char with a string or a string with a char. They are used as:
var str="Visit Microsoft!";
var n=str.replace("Microsoft","W3Schools");
Your code:
var from=10, to=17;
//...
var stringGot = str.replace(str.substring(from, to), replace_string);
What you should do will be to split the code first, and then replace the second a letter! As you want one in your example. Thats one way!
First, split the string! And then replaced the second a letter with z.
For String.Replace refer this: http://www.w3schools.com/jsref/jsref_replace.asp
For String.SubString: http://www.w3schools.com/jsref/jsref_substring.asp
For String.Split: http://www.w3schools.com/jsref/jsref_split.asp

Strings are immutable. This means they do not change after they are first instantiated. Every method to manipulate a string actually returns a new instance of a string. So you have to assign your result back to the variable like this:
str = str.replace(str.substring(from, to), replace_string);
Update: However, the more efficient way of doing this in the first place would be the following. it is also less prone to errors:
str = str.substring(0, from) + replace_string + str.substring(to);
See this fiddle: http://jsfiddle.net/cFtKL/
It runs both of the commands through a loop 100,000 times. The first takes about 75ms whereas the latter takes 20ms.

vb6's mid equivalent for jquery

in vb6 there was a very handy function for string manipulation which could put a character at a certain position of another string and i'm looking for an extended jquery equivalent.
let's say i'm having this string:
var mystring = "__1__";
when applying the function:
var mystring = mid(mystring,4,"x");
it should return __1x_
another example:
var mystring = "";
var mystring = mid(mystring,5,"x");
should return: ____5
i know it requires string manipulation using substr but i was wondering if there's a more elegant way?
thanks

This can be simulated in several ways although there is no such specific function (splice is standard only on Arrays, not Strings).
The easiest one-expression way I know of is with a String.replace when adding to a location "past the end of the string" is not required. Of course String.slice is also a perfectly valid approach, and may be arguably easier to understand.
mystring = "__1__"
// where 3 represents the "characters to skip before inserting"
// and 1 represents the "number of characters to replace"
midstr = mystring.replace(/([^]{3})[^]{0,1}/, "$1x")
Neither the above nor a basic slice will work like the 2nd example without additional prepend-as-needed logic.

String manipulation - getting value after the last position of a char

How I can get the value after last char(. ; + _ etc.):
e.g.
string.name+org.com
I want to get "com".
Is there any function in jQuery?

Use lastIndexOf and substr to find the character and get the part of the string after it:
var extension = name.substr(name.lastIndexOf(".") + 1);
Demo: http://jsfiddle.net/Guffa/K3BWn/

A simple and readable approch to get the substring after the last occurrence of a character from a defined set is to split the string with a regular expression containing a character class and then use pop() to get the last element of the resulting array:
The pop() method removes the last element from an array and returns that element.
See a JS demo below:
var s = 'string.name+org.com';
var result = s.split(/[.;+_]/).pop();
console.log(result);
to split at all non-overlapping occurrences of the regex by default.
NOTE: If you need to match ^, ], \ or -, you may escape them and use anywhere inside the character class (e.g. /[\^\-\]\\]/). It is possible to avoid escaping ^ (if you do not put it right after the opening [), - (if it is right after the opening [, right before the closing ], after a valid range, or between a shorthand character class and another symbol): /[-^\]\\]/.
Also, if you need to split with a single char, no regex is necessary:
// Get the substring after the last dot
var result = 'string.name+org.com'.split('.').pop();
console.log(result);

Not jQuery, just JavaScript: lastIndexOf and substring would do it (not since the update indicating multiple characters). As would a regular expression with a capture group containing a character class followed by an end-of-string anchor, e.g. /([^.;+_]+)$/ used with RegExp#exec or String#match.
E.g. (live copy | source):
var match = /([^.;+_]+)$/.exec(theStringToTest),
result = match && match[1];

var s = "string.name+org.com",
lw = s.replace(/^.+[\W]/, '');
console.log(lw) /* com */
this will also work for
string.name+org/com
string.name+org.info

You can use RegExp Object.
Try this code:
"http://stackoverflow.com".replace(/.*\./,"");

I'll throw in a crazy (i.e. no RegExp) one:
var s = 'string.name+org.com';
var a = s.split('.'); //puts all sub-Strings delimited by . into an Array
var result = a[a.length-1]; //gets the last element of that Array
alert(result);​
EDIT: Since the update of the question is demanding mutiple delimiters to work this is probably not the way to go. Too crazy.....

use javascript function like
url.substr(url.length - 3);

maybe this is too late to consider, this codes works fine for me using jquery
var afterDot = value.substr(value.lastIndexOf('_') + 1);
You could just replate '_' to '.'
var myString = 'asd/f/df/xc/asd/test.jpg'
var parts = myString.split('/');
var answer = parts[parts.length - 1];
console.log(answer);

JavaScript - How to get at specific value in a string?

I have a string from which I am trying to get a specif value. The value is buried in the middle of the string. For example, the string looks like this:
Content1Save
The value I want to extract is "1";
Currently, I use the built-in substring function to get to remove the left part of the string, like this:
MyString = "Content1Save";
Position = MyString;
Position = Position.substring(7);
alert(Position); // alerts "1Save"
I need to get rid of the "Save" part and be left with the 1;
How do I do that?
+++++++++++++++++++++++++++++++++++++++++
ANSWER
Position = Position.substr(7, 1);
QUESTION
What's the difference between these two?
Position = Position.substr(7, 1);
Position = Position.substring(7, 1);

You can use the substr[MDN] method. The following example gets the 1 character long substring starting at index 7.
Position = Position.substr(7, 1);
Or, you can use a regex.
Position = /\d+/.exec(Position)[0];

I would suggest looking into regex, and groups.
Regex is built essentially exactly for this purpose and is built in to javascript.
Regex for something like Content1Save would look like this:
rg = /^[A-Za-z]*([0-9]+)[A-Za-z]*$/
Then you can extract the group using:
match = rg.exec('Content1Save');
alert(match[1]);
More on regex can be found here: http://en.wikipedia.org/wiki/Regular_expression

It highly depends on the rules you have for that middle part. If it's just a character, you can use Position = Position.substring(0, 1). If you're trying to get the number, as long as you have removed the letters before it, you can use parseInt.
alert(parseInt("123abc")); //123
alert(parseInt("foo123bar")); //NaN

If you're actually trying to search, you'll more often than not need to use something called Regular Expressions. They're the best search syntax JavaScript avails.
var matches = Position.match(/\d+/)
alert(matches[0])
Otherwise you can use a series of substr's, but that implies you know what is in the string to begin with:
MyString.substr(MyString.indexOf(1), 1);
But that is a tad annoying.