梁美英 / programming · Files

'use strict';
var aFunction  = require('./_a-function')
  , isObject   = require('./_is-object')
  , invoke     = require('./_invoke')
  , arraySlice = [].slice
  , factories  = {};

var construct = function(F, len, args){
  if(!(len in factories)){
    for(var n = [], i = 0; i < len; i++)n[i] = 'a[' + i + ']';
    factories[len] = Function('F,a', 'return new F(' + n.join(',') + ')');
  } return factories[len](F, args);
};

module.exports = Function.bind || function bind(that /*, args... */){
  var fn       = aFunction(this)
    , partArgs = arraySlice.call(arguments, 1);
  var bound = function(/* args... */){
    var args = partArgs.concat(arraySlice.call(arguments));
    return this instanceof bound ? construct(fn, args.length, args) : invoke(fn, args, that);
  };
  if(isObject(fn.prototype))bound.prototype = fn.prototype;
  return bound;
};