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

args = f => f.toString ()
    .replace( /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg,'')
    .replace(/(\r\n\t|\n|\r\t)/gm,"")
    .trim()
    .match (/(?:\w*?\s?function\*?\s?\*?\s*\w*)?\s*(?:\((.*?)\)|([^\s]+))/)
    .slice (1,3)
    .join ('').replace(/\s/g, '').
    split (/\s*,\s*/);

/*Test*/
console.log(args((a,b)=>a+b));
console.log(args(function(c,d){return c+d;}));
console.log(args(async function(a,b,c){/**/}));
console.log(args(function* (a,b,c,d){/**/}));
console.log(args(function name(s1,s2){}));
console.log(args(function name(/*comment 1*/ s3/*comment2*/,s4//
){}));
console.log(args(async function* name(/*comment1*/ s5/*comment2*/,s6){}));

console.log(args(async function * name(/*comment1*/ s7/*comment2*/,s8){}));

console.log(args(async function *name(/*comment1*/ s9/*comment2*/,s10){}));

Answer 2

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.