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

Asked 2011-08-03T04:21:28.063
29

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 not, is it possible to get the number of arguments? For example, in PHP, one could use:

$class = new ReflectionClass('classNameHere');
$methods = $class->getMethods();
foreach ($methods as $method) {
    print_r($method->getParameters());
}

... or something like that, I haven't touched PHP in a while so the example above may not be correct.

Thanks in advance!

EDIT: Unfortunately, I have to be able to get the arguments outside of the body of the function... Sorry for the lack of clarification, but thanks for the current answers!

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1 Answer

18

it is possible get all the formal parameter name of a javascript:

var FN_ARGS = /^function\s*[^\(]*\(\s*([^\)]*)\)/m;
var FN_ARG_SPLIT = /,/;
var FN_ARG = /^\s*(_?)(\S+?)\1\s*$/;
var STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;

function formalParameterList(fn) {
   var fnText,argDecl;
   var args=[];
   fnText = fn.toString().replace(STRIP_COMMENTS, '');
   argDecl = fnText.match(FN_ARGS); 

   var r = argDecl[1].split(FN_ARG_SPLIT);
   for(var a in r){
      var arg = r[a];
      arg.replace(FN_ARG, function(all, underscore, name){
         args.push(name);
      });
   }
   return args;
 }

this can be tested this way :

 var expect = require('expect.js');
 expect( formalParameterList(function() {} )).to.eql([]);
 expect( formalParameterList(function () {} )).to.eql([]);
 expect( formalParameterList(function /*  */ () {} )).to.eql([]);
 expect( formalParameterList(function (/* */) {} )).to.eql([]);
 expect( formalParameterList(function ( a,   b, c  ,d /* */, e) {} )).to.eql(['a','b','c','d','e']);

Note: This technique is use with the $injector of AngularJs and implemented in the annotate function. (see https://github.com/angular/angular.js/blob/master/src/auto/injector.js and the corresponding unit test in https://github.com/angular/angular.js/blob/master/auto/injectorSpec.js )

answered 2012-12-01T14:59:53.993

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