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How to compare two Strings and get Different part

now I have two strings,
var str1 = "A10B1C101D11";
var str2 = "A1B22C101D110E1";
What I intend to do is to tell the difference between them, the result will look like
A10B1C101D11
A10 B22 C101 D110E1
It follows the same pattern, one character and a number. And if the character doesn't exist or the number is different between them, I will say they are different, and highlight the different part. Can regular expression do it or any other good solution? thanks in advance!

Let me start by stating that regexp might not be the best tool for this. As the strings have a simple format that you are aware of it will be faster and safer to parse the strings into tokens and then compare the tokens.
However you can do this with Regexp, although in javascript you are hampered by the lack of lookbehind.
The way to do this is to use negative lookahead to prevent matches that are included in the other string. However since javascript does not support lookbehind you might need to go search from both directions.
We do this by concatenating the strings, with a delimiter that we can test for.
If using '|' as a delimiter the regexp becomes;
/(\D\d*)(?=(?:\||\D.*\|))(?!.*\|(.*\d)?\1(\D|$))/g
To find the tokens in the second string that are not present in the first you do;
var bothstring=str2.concat("|",str1);
var re=/(\D\d*)(?=(?:\||\D.*\|))(?!.*\|(.*\d)?\1(\D|$))/g;
var match=re.exec(bothstring);
Subsequent calls to re.exec will return later matches. So you can iterate over them as in the following example;
while (match!=null){
alert("\""+match+"\" At position "+match.index);
match=re.exec(t);
}
As stated this gives tokens in str2 that are different in str1. To get the tokens in str1 that are different use the same code but change the order of str1 and str2 when you concatenate the strings.
The above code might not be safe if dealing with potentially dirty input. In particular it might misbehave if feed a string like "A100|A100", the first A100 will not be considered as having a missing object because the regexp is not aware that the source is supposed to be two different strings. If this is a potential issue then search for occurences of the delimiting character.

You call break the string into an array
var aStr1 = str1.split('');
var aStr2 = str2.split('');
Then check which one has more characters, and save the smaller number
var totalCharacters;
if(aStr1.length > aStr2.length) {
totalCharacters = aStr2.length
} else {
totalCharacters = aStr1.length
}
And loop comparing both
var diff = [];
for(var i = 0; i<totalCharacters; i++) {
if(aStr1[i] != aStr2[i]) {
diff.push(aStr1[i]); // or something else
}
}
At the very end you can concat those last characters from the bigger String (since they obviously are different from the other one).
Does it helps you?

javascript regex to extract the first character after the last specified character

I am trying to extract the first character after the last underscore in a string with an unknown number of '_' in the string but in my case there will always be one, because I added it in another step of the process.
What I tried is this. I also tried the regex by itself to extract from the name, but my result was empty.
var s = "XXXX-XXXX_XX_DigitalF.pdf"
var string = match(/[^_]*$/)[1]
string.charAt(0)
So the final desired result is 'D'. If the RegEx can only get me what is behind the last '_' that is fine because I know I can use the charAt like currently shown. However, if the regex can do the whole thing, even better.

If you know there will always be at least one underscore you can do this:
var s = "XXXX-XXXX_XX_DigitalF.pdf"
var firstCharAfterUnderscore = s.charAt(s.lastIndexOf("_") + 1);
// OR, with regex
var firstCharAfterUnderscore = s.match(/_([^_])[^_]*$/)[1]
With the regex, you can extract just the one letter by using parentheses to capture that part of the match. But I think the .lastIndexOf() version is easier to read.
Either way if there's a possibility of no underscores in the input you'd need to add some additional logic.

Javascript string validation using the regex object

I am complete novice at regex and Javascript. I have the following problem: need to check into a textfield the existence of one (1) or many (n) consecutive * (asterisk) character/characters eg. * or ** or *** or infinite (n) *. Strings allowed eg. *tomato or tomato* or **tomato or tomato** or as many(n)*tomato many(n)*. So, far I had tried the following:
var str = 'a string'
var value = encodeURIComponent(str);
var reg = /([^\s]\*)|(\*[^\s])/;
if (reg.test(value) == true ) {
alert ('Watch out your asterisks!!!')
}

By your question it's hard to decipher what you're after... But let me try:
Only allow asterisks at beginning or at end
If you only allow an arbitrary number (at least one) of asterisks either at the beginning or at the end (but not on both sides) like:
*****tomato
tomato******
but not **tomato*****
Then use this regular expression:
reg = /^(?:\*+[^*]+|[^*]+\*+)$/;
Match front and back number of asterisks
If you require that the number of asterisks at the biginning matches number of asterisks at the end like
*****tomato*****
*tomato*
but not **tomato*****
then use this regular expression:
reg = /^(\*+)[^*]+\1$/;
Results?
It's unclear from your question what the results should be when each of these regular expressions match? Are strings that test positive to above regular expressions fine or wrong is on you and your requirements. As long as you have correct regular expressions you're good to go and provide the functionality you require.
I've also written my regular expressions to just exclude asterisks within the string. If you also need to reject spaces or anything else simply adjust the [^...] parts of above expressions.
Note: both regular expressions are untested but should get you started to build the one you actually need and require in your code.

If I understand correctly you're looking for a pattern like this:
var pattern = /\**[^\s*]+\**/;
this won't match strings like ***** or ** ***, but will match ***d*** *d or all of your examples that you say are valid (***tomatos etc).If I misunderstood, let me know and I'll see what I can do to help. PS: we all started out as newbies at some point, nothing to be ashamed of, let alone apologize for :)
After the edit to your question I gather the use of an asterisk is required, either at the beginning or end of the input, but the string must also contain at least 1 other character, so I propose the following solution:
var pattern = /^\*+[^\s*]+|[^\s*]+\*+$/;
'****'.match(pattern);//false
' ***tomato**'.match(pattern);//true
If, however *tomato* is not allowed, you'll have to change the regex to:
var pattern = /^\*+[^\s*]+$|^[^\s*]+\*+$/;
Here's a handy site to help you find your way in the magical world of regular expressions.

Whats the best way to get an id from a URL written in different ways?

I'm trying to find a quick way to get an ID from a url like this in javascript or jquery?
https://plus.google.com/115025207826515678661/posts
https://plus.google.com/115025207826515678661/
https://plus.google.com/115025207826515678661
http://plus.google.com/115025207826515678661/posts
http://plus.google.com/115025207826515678661/
http://plus.google.com/115025207826515678661
plus.google.com/115025207826515678661/posts
plus.google.com/115025207826515678661/
plus.google.com/115025207826515678661
want to just get 115025207826515678661 from the URL
Is there a sure way to always get the ID regardless of the way its typed?

You could use this javascript which works on all the urls you posted:
var url, patt, matches, id;
url = 'https://plus.google.com/115025207826515678661/posts';
patt = /\/(\d+)(?:\/|$)/
matches = patt.exec(url);
id = matches[1];

Use the following regular expression to extract the value:
\/([0-9]+)\/?
Tested on all of your input strings and it worked on each.
The first and only group will have the number you're looking for

var pos=url.indexOf('com').
var str1=url.substr(pos+3,21);
if the 21 is not constant, then just check the indexOf('/') in the substr:
var pos=url.indexOf('com').
var str1=url.substr(pos+3);
pos=str1.indexOf('/');
var str2=str1.substr(0,pos);
alert(str2);
or, use some regexp magic as was written in a different answer here.

I believe you could create a new string, and then loop through the URL string, and copy any numbers into the new string, especially if the URLs never have other numerical characters.
Basically, stripping all but numerical characters.

Javascript regex match for string "game_1"

I just can't get this thing to work in javascript. So, I have a text "game_1" without the quotes and now i want to get that number out of it and I tried this:
var idText = "game_1";
re = /game_(.*?)/;
found = idText.match(re);
var ajdi = found[1];
alert( ajdi );
But it doesn't work - please point out where am I going wrong.

If you're only matching a number, you may want to try
/game_([0-9]+)/
as your regular expression. That will match at least one number, which seems to be what you need. You entered a regexp that allows for 0 characters (*) and let it select the shortest possible result (?), which may be a problem (and match you 0 characters), depending on the regex engine.

If this is the complete text, then there is no need for regular expressions:
var id = +str.split('_')[1];
or
var id = +str.replace('game_', '');
(unary + is to convert the string to a number)
If you insist on regular expression, you have to anchor the expression:
/^game_(.*?)$/
or make the * greedy by omitting the ?:
/game_(.*)/
Better is to make the expression more restrictive as #Naltharial suggested.

Simple string manipulation:
var idText = "game_1",
adji = parseInt(idText.substring(5), 10);

* means zero or more occurrences. It seems that combining it with a greediness controller ? results in zero match.
You could replace * with + (which means one or more occurrences), but as #Felix Kling notes, it would only match one digit.
Better to ditch the ? completely.
http://jsfiddle.net/G8Qt7/2/

Try "game_1".replace(/^(game_)/, '')
this will return the number

You can simply use this re /\d+/ to get any number inside your string