fiddling around with the `arguments` construct in .js

partials.js

// takes a fn and a number of arguments to append to the 
// fn's argument list
var rPartial = function(fn, extras) {
  var postArgs = [].slice.call(arguments).slice(1);
  return function(vars) { 
    var preArgs = [].slice.call(arguments);
    var allArgs = preArgs.concat(postArgs);
    return fn.call(fn.this, ...allArgs); 
  };
}

// takes a fn and a number of arguments to prepend to
// the fn's argument list
var lPartial = function(fn, extras) {
  var preArgs = [].slice.call(arguments).slice(1);
  return function(vars) {
    var postArgs = [].slice.call(arguments);
    var allArgs = preArgs.concat(postArgs);
    return fn.call(fn.this, ...allArgs); 
  };
}

// returns the argument list, for demonstration
var flog = function(args) { 
  return [].slice.call(arguments); 
}

var ary = [0,1,2,3,4];

var rflog = rPartial(flog, 5, 6);
var lflog = lPartial(flog, 5, 6);
console.log(lflog(...ary));
console.log(rflog(...ary));