Parsing Node Command Line Arguments

I am learning how to use node.js, but am having trouble parsing command-line arguments. The following line:

node test.js --input=in.txt

Gives a parsing error when the code reaches this command:

var fileName = JSONparse.(process.argv[2]);

Results in the error:

 undefined
--input=in.txt 

Syntax error: Unexpected number

What I am trying to do is create an optional variable for the input file. If it is not specified in the command-line, it should resolve to 'a.txt'.

I have not found an easy way of creating default parameters, or use identifiers such as '--input=' to not have to worry about the order in which arguments are passed (I know it does not matter in this case with one argument).