How to get function parameter names/values dynamically?

Question

Is there a way to get the function parameter names of a function dynamically?

Let’s say my function looks like this:

function doSomething(param1, par         


        

Answer 1

Here is an updated solution that attempts to address all the edge cases mentioned above in a compact way:

function $args(func) {  
    return (func + '')
      .replace(/[/][/].*$/mg,'') // strip single-line comments
      .replace(/\s+/g, '') // strip white space
      .replace(/[/][*][^/*]*[*][/]/g, '') // strip multi-line comments  
      .split('){', 1)[0].replace(/^[^(]*[(]/, '') // extract the parameters  
      .replace(/=[^,]+/g, '') // strip any ES6 defaults  
      .split(',').filter(Boolean); // split & filter [""]
}  

Abbreviated test output (full test cases are attached below):

'function (a,b,c)...' // returns ["a","b","c"]
'function ()...' // returns []
'function named(a, b, c) ...' // returns ["a","b","c"]
'function (a /* = 1 */, b /* = true */) ...' // returns ["a","b"]
'function fprintf(handle, fmt /*, ...*/) ...' // returns ["handle","fmt"]
'function( a, b = 1, c )...' // returns ["a","b","c"]
'function (a=4*(5/3), b) ...' // returns ["a","b"]
'function (a, // single-line comment xjunk) ...' // returns ["a","b"]
'function (a /* fooled you...' // returns ["a","b"]
'function (a /* function() yes */, \n /* no, */b)/* omg! */...' // returns ["a","b"]
'function ( A, b \n,c ,d \n ) \n ...' // returns ["A","b","c","d"]
'function (a,b)...' // returns ["a","b"]
'function $args(func) ...' // returns ["func"]
'null...' // returns ["null"]
'function Object() ...' // returns []

function $args(func) {  
    return (func + '')
      .replace(/[/][/].*$/mg,'') // strip single-line comments
      .replace(/\s+/g, '') // strip white space
      .replace(/[/][*][^/*]*[*][/]/g, '') // strip multi-line comments  
      .split('){', 1)[0].replace(/^[^(]*[(]/, '') // extract the parameters  
      .replace(/=[^,]+/g, '') // strip any ES6 defaults  
      .split(',').filter(Boolean); // split & filter [""]
}  

// test cases  
document.getElementById('console_info').innerHTML = (
[  
  // formatting -- typical  
  function(a,b,c){},  
  function(){},  
  function named(a, b,  c) {  
/* multiline body */  
  },  
    
  // default values -- conventional  
  function(a /* = 1 */, b /* = true */) { a = a||1; b=b||true; },  
  function fprintf(handle, fmt /*, ...*/) { },  
  
  // default values -- ES6  
  "function( a, b = 1, c ){}",  
  "function (a=4*(5/3), b) {}",  
  
  // embedded comments -- sardonic  
  function(a, // single-line comment xjunk) {}
    b //,c,d
  ) // single-line comment
  {},  
  function(a /* fooled you{*/,b){},  
  function /* are you kidding me? (){} */(a /* function() yes */,  
   /* no, */b)/* omg! */{/*}}*/},  
  
  // formatting -- sardonic  
  function  (  A,  b  
,c  ,d  
  )  
  {  
  },  
  
  // by reference  
  this.jQuery || function (a,b){return new e.fn.init(a,b,h)},
  $args,  
  
  // inadvertent non-function values  
  null,  
  Object  
].map(function(f) {
    var abbr = (f + '').replace(/\n/g, '\\n').replace(/\s+|[{]+$/g, ' ').split("{", 1)[0] + "...";
    return "    '" + abbr + "' // returns " + JSON.stringify($args(f));
  }).join("\n") + "\n"); // output for copy and paste as a markdown snippet