Is it possible to reflect the arguments of a Javascript function?

Question

Is it possible to get all of the arguments a Javascript function is written to accept? (I know that all Javascript function arguments are \"optional\")? If

Answer 1

This new version handles fat arrow functions as well...

args = f => f.toString ().replace (/[\r\n\s]+/g, ' ').
              match (/(?:function\s*\w*)?\s*(?:\((.*?)\)|([^\s]+))/).
              slice (1,3).
              join ('').
              split (/\s*,\s*/);

function ftest (a,
                 b,
                 c) { }

let aftest = (a,
                 b,
                 c) => a + b / c;

console.log ( args (ftest),  // = ["a", "b", "c"] 
              args (aftest), // = ["a", "b", "c"]
              args (args)    // = ["f"]
             );

Here is what I think you are looking for :

 function ftest (a,
                 b,
                 c) { }
 var args = ftest.toString ().
              replace (/[\r\n\s]+/g, ' ').
              match (/function\s*\w*\s*\((.*?)\)/)[1].split (/\s*,\s*/);

args will be an array of the names of the arguments of test i.e. ['a', 'b', 'c']

The value is args will be an array of the parameter names if the ftest is a function. The array will be empty if ftest has not parameters. The value of args will be null if ftest fails the regular expression match, i.e it is not a function.