1. 自定义原型方法去重

// 字符串去重
String.prototype.unique = function(){
  var obj = {},
      str = '';
  for(var i = 0; i < this.length; i++){
    var item = this[i];
    if(!obj.hasOwnProperty(item)){
      obj[item] = item;
      str += item;
    }
  }                                
  return str;                                                                                
}
var str = 'dasdasfdafsd1232312dasdasfgsdg';
var str1 = str.unique();
console.log(str1);

// 计算字符出现次数
String.prototype.strCount = function(){
  var obj = {};
  for(var i = 0; i < this.length; i++){
    var item = this[i];
    if(!obj.hasOwnProperty(item)){
      obj[item] = 1;
    }else{
      obj[item]++;
    }
  }
  return obj;
}
var str = '1111asdasdashellohell';
var obj = str.strCount();
console.log(obj);

2. 面试题

function Test(a, b, c) {
  var d = 0;
  this.a = a;
  this.b = b;
  this.c = c;
  function e() {
    d++;
    console.log(d);
  }
  this.f = e;
}
// GO = {
//   Test: function(){},
//   test1: undefined => new Test(),
//   test2: undefined => new Test()
// }
// Test.AO = {
//   d: undefined => 0,
//   e: function e(){},
// }
// f.AO => e.AO = {
//
// }
var test1 = new Test();
test1.f(); // 1
test1.f(); // 2
var test2 = new Test();
test2.f(); // 1

function test(){
  console.log(typeof(arguments)); // object
}
test(1, 2, 3, 4);

var test = function a(){ // 函数表达式的名字会被忽略
  console.log(a); // 内部可以访问
  console.log(test.name); // a
}
// console.log(a); // 外部会报错undefined
console.log(typeof(a)); // undefined
console.log(test.name); // a 
test();

// 判断星期几
function test(day){
  var weekday = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
  return weekday[day - 1] !== undefined ? console.log(weekday[day])
                                    : console.log('I don\'t know');
}
test(0);
test(1);
// 不用 day - 1,利用数组逗号加empty特性
function test(day){
  var weekday = [,'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
  return weekday[day] !== undefined ? console.log(weekday[day])
                                    : console.log('I don\'t know');
}
test(0);
test(1);