改变上下文bind apply call

bind 返回一个函数， call apply 直接执行。

// bind
if ( !Function.prototype.bind ){
Function.prototype.bind = function(context){
  if ( typeof this !== 'function' ){
    console.log('this is not function');
    throw new Error('this is not function');
    return ;
  }

  var args = Array.prototype.slice.call(arguments, 1),
      self = this;
  var tmpFunc = function(){};           // 构造函数原型链继承
  var mainFunc = function(){
      var innerArgs = Array.prototype.slice.call(arguments);  //改变上下文之后的arguments
      var finalArgs = args.concat(innerArgs);
      return self.apply(this instanceof tmpFunc ? this : context || window,finalArgs);
  };

  tmpFunc.prototype = this.prototype;
  mainFunc.prototype = new tmpFunc();
  return mainFunc;
};
}

// call, apply
Function.prototype.call = function(context){
  var context = context || window;
  context.fn = this;
  var args = [];
  for ( var i=0,len=arguments.length; i<len; i++ ){
    args.push('arguments['+i+']');
  }

  var res = eval('context.fn('+args+')');
  delete conetxt.fn;
  return res;
}

// apply
Function.prototype.apply = function(context, argArr){
  var context = context || window;
  if ( !arr ) return this();

  context.fn = this;

  var args = [];
  for ( var i=0,len=argArr.length; i<len; i++ ){
    args.push('argArr['+i+']');
  }

  var res = eval('context.fn('+args+')');
  delete conetxt.fn;
  return res;
}