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
As has been said, it's an empty JavaScript object.

What's not so obvious I guess is *why* you would do that. A common reason is to make your code safe if the object happens to be `null` or `undefined`. Consider the example where you are passed an object and want to access an attribute of it:

```
function myFunc(obj) {
    console.log(obj.name);
}

```

That's fine, unless `obj` is `undefined`, in which case your code will crash.

A safer way is often:

```
function myFunc(obj) {
    console.log((obj || {}).name);
}

```

Now if `obj` is `undefined` then a new empty object is created instead. Getting the `.name` of that is safe and will simply return `undefined`.

This is obviously an over-simplified example, but the technique is widely used to make code shorter and easier to read (less tests and branches than putting `if` statements everywhere).