call function dynamically with indefinite # of arguments #js

dynamic_fn.js

function execFn( fn ) {
  var context;
  // check passed in 'this' a.k.a. 'arguments[0]' & set context
  context = ( typeof this === "undefined" || typeof this === "null" )
            ? window
            : this;
  // locate 'fn' in 'context' or it's a raw function
  fn = ( typeof fn === "function" )
       ? fn
       : context[fn];
  // pass on arguments and call the 'fn'
  fn.apply( context, Array.prototype.slice.call( arguments, 1 ) ); // shift first and pass rest
};

// -------
// USAGE:
// -------

testFn =  function (a,b) { console.log( a, b, "WOW!" );  }
obj = { locate: function( emoticon ) { console.log( this.secret, emoticon );  }, secret: "TREASURE" };

execFn( "testFn", "5", {a:2} ); // 5 Object WOW!
execFn( testFn, 7, {a:3} ); // 7, Object "WOW!"
execFn( "locate", ":-O" ); // TypeError: Cannot call method 'apply' of undefined
execFn.call( obj, "locate", ":-O" ); // TREASURE :-O
execFn.bind( obj )( "locate", ":-)" ); // TREASURE :-)