Creating Regex with literal backslash

Backslash in Regex has special meanings. So how do I create a Regex expression that contains a literal backslash.

It is quite simple. Just use "\\" instead of "\" in the Regex.

Now come the problem. I need to define a string variable and pass it to a function to create a Regex in the function.

For example, I need to create a string "A\" . The string can be defined as myvar="A\\" in javascript. Up till now it is fine. Now if I set

myRegex=new RegExp("^"+myvar,"")

in the function and test it, the script crashes.

It turned out that I must define the string as myvar="A\\\\" so that the RegExp can see the string as "A\\" and parse it as a literal "A\".

So much trouble to just create a backslash in Regex.