Question: I am trying to extract a string in this format **"[\r\n \"MG480612230220150018\"\r\n]"** using regex, i am trying to match number and alphabet with a min length of 5 character but it is not working, therefore i can guarantee i will extract this data (**MG480612230220150018**)

```
        Regex regex = new Regex(@"^[0-9a-zA-Z]{5,}$");
        Match match = regex.Match(availability.Id.ToString());
        if (match.Success)
        {
            var myid = match.Value;
        }

```

Answer: 
This is used to define a variable if it is not set.
You can do this to ensure there is a value set!

for example:

```
function iHaveParameters(param1, param2) {
   param1 = param1 || {} //empty object
   param2 = param2 || "This should be a string"
}

```

And of course as noted, it will only invoke the second value when the first variable is null.

And in your case it is actually only setting the variable when it's not set, meaning if you include the script 3000 times, the variable will only still be defined once avoiding CPU. This way you could require the loading of a function for example
It means: if the object before `||` is null, use a new empty object `{}` instead.

Read more about the operator here: [Is there a "null coalescing" operator in JavaScript?](https://stackoverflow.com/questions/476436/is-there-a-null-coalescing-operator-in-javascript)