JavaScript - 变量、值、类型

摘要：一返回值共有种二变量声明方法声明一个变量，可以将其初始化为一个值声明一个块级作用域变量，可以将其初始化一个值声明一个只读的常量使用的注意事项不支持块级作用域存在变量提升举例由于变量声明提升，这段代码相当于使用的注意事项块级作用域

返回值共有7种：undefined, object, boolean, number, string, symbol, function

typeof undefined === "undefined";
typeof true === "boolean";
typeof 123 === "number";
typeof "username" === "string";
typeof {team : "75team"} === "object"
typeof symbol() === "symbol";
typeof null === "object";
typeof function() {} === "function";

var - 声明一个变量，可以将其初始化为一个值
const - 声明一个块级作用域变量，可以将其初始化一个值
let - 声明一个只读的常量

var不支持块级作用域

var存在变量提升

举例：

console.log(a === undefined);
var a = 10;

function foo(){
  console.log([a, i]);
  var a = 20;
  for(var i = 0; i < a; i++){
    //do sth.
  }
  console.log([a, i]);
}
foo();

//---console:
true
[undefined, undefined]
[20, 20]

由于变量声明提升，这段代码相当于

var a;
console.log(a === undefined);
a = 10;

function foo(){
  var a, i;
  console.log([a, i]);
  a = 20;
  for(i = 0; i < a; i++){
    //do sth.
  }
  console.log([a, i]);
}
foo();

块级作用域

同一个作用域下只能声明一次

暂存死区(temporal dead zone)

循环中的let作用域

浏览器兼容性

块级作用域示例：

{
  let x = 10;

  console.log("x is " + x);
}

console.log(typeof x);

let i = 20;

for(let i = 0; i < 10; i++){
  console.log(i);
}
console.log(i);

var y = 3;
var y = 4;

console.log(y);

// let z = 3;
// var z = 4;
// console.log(z);

//---console:

"x is 10"
"undefined"
0
1
2
3
4
5
6
7
8
9
20
4

暂存死区示例：

let x = 10;

function foo(){
  console.log(x);
  let x = 20;  //如果这一句改成 var 会怎样？
  return x * x;
}

console.log(foo());

//---console:
"ReferenceError: x is not defined"

循环中的let作用域示例:

var buttons = document.querySelectorAll("button");

for(var i = 0; i < buttons.length; i++){
  buttons[i].onclick = evt => console.log("点击了第 " + i + "个按钮");
}

//---console:
"点击了第 5个按钮"
"点击了第 5个按钮"
"点击了第 5个按钮"
"点击了第 5个按钮"

这里是因为click这个方法是异步的，只有在点击之后，js才会去执行这段代码，这时for循环中的 i 已经循环完，所以会产生点击哪个按钮都返回 5 。解决这类问题常利用‘闭包’，或者使用let

var buttons = document.querySelectorAll("button");

for(var i = 0; i < buttons.length; i++){
  (function (i) {
       buttons[i].onclick = evt => console.log("点击了第 " + i + "个按钮");
  })(i)
}

const声明的变量不可以再次被改变

其他使用与let一样

示例：

const BUFFER_SIZE = 1024;

let buffer = new ArrayBuffer(BUFFER_SIZE);

console.log(buffer);

let data = new Uint16Array(buffer);
let data2 = new Uint8Array(buffer);

data[0] = 0xff06;

console.log(data2[0], data2[1]);

//---console:
[object ArrayBuffer]
6
255

注意：给变量赋值为对象时，对象引用不能变，但是对象里的属性值可以改变。

// A的地址没有改变，这样也是可以的。
const A = {a: 1};
A.a = 2;
console.log(A); 
// A: {a: 2}

// 如何不让A被操作呢？
const A = Object.freeze({a: 1});
A.a = 2;
console.log(A); 
// A: {a: 1}

(function(){
  //"use strict";
  
  var x = y = 0;
  
  //do sth.
})();

console.log([typeof x, typeof y]);

//---console:
["undefined", "number"]

但是在ES6与‘use strict’某些时候会有冲突

(function f( j = 777 ) {
    "use strict";
    // do sth.
})


ERROR: Uncaught SyntaxError: Illegal "use strict" directive in function with non-simple parameter list

javascript

console.log([null !== undefined, null == undefined]); //true, true

console.log(["1" == 1, [] == 0, "" == 0, 0 == false, 1 == true]);

console.log([NaN != NaN]);

Console

[true, true]
[true, true, true, true, true]
[true]

true 和 false

0、""、null、undefined 被隐式转换为 false，其他转为 true

建议采用严格比较，可以通过 !! 将非 boolean 值转为 boolean

布尔操作符 && 和 || 并不会转换类型

&& 和 || 的短路特性

比较操作符总是返回 boolean 类型

javascript

var result = 1 && 2;

console.log([result, !!result]);

var list = [1,,2,,,4,5,0,9];

list = list.filter(item => item);

console.log(list);

function showTip(tip){
  tip = tip || "This is a tip";
  console.log(tip);
  
  var label = document.createElement("label");
  label.className = "tip";
  label.innerHTML = tip;
  
  document.body.appendChild(label);
}

document.querySelector("button").onclick 
  = showTip.bind(null, "");

console

"This is a tip"
"This is a tip"
"This is a tip"
...

示例2：
JavaScript

/**
 * options -> type:x、y、xy or function
 */
function applyAnimate(el, duration, options, easing){
  var startTime = Date.now();
  if(typeof el === "string"){
    el = document.querySelector(el);
  }
  duration = duration || 1000;
  options = options || {
    property: "x",
    distance: 100
  };
  easing = easing || function(p){return p;};

  requestAnimationFrame(function update(){
    var now = Date.now();
    var p = (now - startTime)/duration;
    var ep = easing(p); 

    if(typeof options !== "function"){
      var attr = options.property, distance = options.distance;
      var translate = [];
      if(attr.indexOf("x") >= 0){
        translate.push("translateX(" + distance * ep + "px)");
      }
      if(attr.indexOf("y") >= 0){
        translate.push("translateY(" + distance * ep + "px)");
      }
      el.style.transform = translate.join(" ");
    }else{
      options(el, ep, p);
    }
    
    if(p <= 1){
      requestAnimationFrame(update);
    }
  });
}

document.querySelector(".ball").onclick = function(){

  applyAnimate(".ball");

  /*applyAnimate(".ball", 1000, function(el, ep, p){
  const distance = 100, pi2 = 2 * Math.PI;
  el.style.transform = "translate(" + distance * Math.cos(pi2 * ep) 
    + "px," + distance * Math.sin(pi2 * ep)  + "px)";
});*/
}

整数 -2^53 ~ 2^53

小数精度 Number.EPSILON

Infinity、Number.MAX_VALUE、Number.MIN_VALUE

浮点数有精度问题

2进制，8进制，十六进制

+0和-0

javascript

//-----------

console.log(0.2 + 0.4); //WTF!! IEEE754

console.log(((0.2 + 0.4) * 100).toPrecision(2));

console.log(((0.2 + 0.4) * 100).toFixed(2));

//----------

const ball = document.getElementById("ball");

var distance = 100, duration = 2000;

ball.onclick = function(){
  var startTime = Date.now();
  requestAnimationFrame(function update(){
    var p = (Date.now() - startTime) / duration;
  
    ball.style.transform = "translateX(" + distance * p + "px)"
    console.log(p,distance);
    if(p <= 1){ //不应当用相等比较浮点数！！
      requestAnimationFrame(update);
    }
  });
}

console

0.6000000000000001
"60"
"60.00"

示例2：
JavaScript

console.log([Number.MAX_SAFE_INTEGER, Number.MIN_SAFE_INTEGER]);

var bigInteger = Number.MAX_SAFE_INTEGER + 1;

console.log([bigInteger, bigInteger + 1, bigInteger + 2]); //WTF!!

console.log(1234567890000000000000000000); //科学计数法

console.log(Math.pow(2, 53) === bigInteger);

console.log([Number.isSafeInteger(bigInteger), 
             Number.isSafeInteger(bigInteger - 1)]);

//-----------

console.log([Number.MAX_VALUE, Number.MIN_VALUE]);

console.log([Number.MAX_VALUE + 1, Number.MAX_VALUE * 2]);

console.log([Number.EPSILON]);

console.log(0.99 - 1e-17 === 0.99);

console.log(0.99 - Number.EPSILON === 0.99);

console

[9007199254740991, -9007199254740991]
[9007199254740992, 9007199254740992, 9007199254740994]
1.23456789e+27
true
[false, true]
[1.7976931348623157e+308, 5e-324]
[1.7976931348623157e+308, Infinity]
[2.220446049250313e-16]
true
false

引号规范

转义字符

字符串与字符

字符串与类型转换

常用字符串操作

模板字符串

javascript

var text = "This is a text."; //规范建议默认使用双引号
var html = "
This is a paragraph
";

console.log(text);
console.log(html);

var text2 = "我所做的馅饼
是全天下
最好吃的";

console.log(text2);

var text3 = "if(a){
	console.log(b);
}";

console.log(text3);

var text4 = "u5947u821eu56e2";

console.log(text4);

Console

"This is a text."
"
This is a paragraph
"
"我所做的馅饼
是全天下
最好吃的"
"if(a){
  console.log(b);
}"
"奇舞团"

JavaScript

var str = "my string";

console.log(str.charAt(5));

var charArray = Array.from(str); //str.split("");

console.log(charArray);

console.log(str.charCodeAt(5), str.charCodeAt(6));

console.log(String.fromCharCode(114, 105));

console.log(String.fromCharCode(...charArray.map(c=>c.charCodeAt(0))));

Console

"r"
["m", "y", " ", "s", "t", "r", "i", "n", "g"]
114
105
"ri"
"my string"

console.log([1+2, "1"+2, "1"-2]); 
// console: [3, "12", -1]
// 注释：减法不会发生隐式类型转换,可以用减零的方式将字符串转化成数字，如：console.log("1"- 0 + 2);

console.log(parseInt("100abc", 2), Number("0b100")); 
// console: 4 4 
// 转整数

console.log(parseFloat("12.3e10xx")); 
// console: 123000000000
// 转浮点数, parseFloat会尽可能的将字符串中的值转化成浮点数，然后将转化不了的字符串忽略，这里是将“xx”省略。

// 封装对象的 toString 方法
var foo = {
  toString(){
   return "foo"; 
  }
};

console.log(foo + " bar");
// console: "foo bar"

javascript

const a = "hello";
const b = "WORLD";
const c = "!";

console.log(a + " " + b + c); //字符串连接
// 注释：字符串可以用“+”相加，但在某些浏览器内性能不好，可采用数组的join方法拼接字符串。
// console.log([a, b, c].join(""));

console.log(a.toUpperCase() + " " + b.toLowerCase() + c); //转大小写

console.log(a.split("").reverse().join("")); //逆序字符串

console.log([a.slice(2,3), a.substr(2,3)]); //截取子串
// 注释： slice和substr的参数含义不一样

const d = a + " " + b + c;

console.log(d.indexOf(b)); //字符串查找

console.log(d.replace(a, a.toUpperCase()));

Console

"hello WORLD!"
"HELLO world!"
"olleh"
["l", "llo"]
6
"HELLO WORLD!"

const tpl1 = `我所做的馅饼
  是全天下
  最好吃的`;

console.log([tpl1, typeof tpl1]);

{
  let who = "月影", what = "月饼";
  
  const tpl2 = `${who}所做的${what}
    是全天下
    最好吃的`;

  console.log(tpl2);
}

["我所做的馅饼
  是全天下
  最好吃的", "string"]
"月影所做的月饼
    是全天下
    最好吃的"

JavaScript

let output = (a, b) => `${a} + ${b} is ${a + b}`;

console.log(output(3, 5));

let formatedList = (data) => `
  

     ${data.map(item=>`
       
姓名：${item.name}年龄：${item.age}
     `).join("")}
  
`;

let data = [
  {name: "Akira", age: 35},
  {name: "Jane",  age: 26},
  {name: "Jhon",  age: 54}
];

console.log(formatedList(data));

Console

"3 + 5 is 8"
"
  

     
       
姓名：Akira年龄：35
     
       
姓名：Jane年龄：26
     
       
姓名：Jhon年龄：54
     
  
"

对象的属性

值和引用

类型与构造器

内置类型

对象的高级属性

class

属性名规则：可以是有效字符串或者任意可转换为有效字符串的类型​​​​​​​

属性的访问和遍历​​​​​​​

//创建对象
{
  let myObj = new Object();

  myObj.name = "akira";
  myObj.birthday = "12-29";

  console.log(myObj);
}

//然而上面这么写的是菜鸟，普通青年这么写
{
  let myObj = {
    name: "akira",
    birthday: "12-29"
  };
  
  console.log(myObj);
}

//有些二逼青年：
{
  let myObj = Object.create({name: "akira", birthday: "21-29"});
  
  console.log(myObj);
}

javascript

// 对象属性是有效字符串，属性访问可以通过.和[]
{
  let myObj = {
    name: "akira",
    birthday: "12-29"
  };

  console.log([myObj.name, myObj["birthday"]]);
}

{
  // []属性访问的好处是可以计算
  const conf = {
    adapter: "sqlite",
    db: {
      sqlite: {
        //...
      },
      mysql: {
        //...
      }
    }
  }
  let dbSetting = conf.db[conf.adapter];
}

{
  // 在 ES6 中字面量的 key 也支持属性计算
  // 比如可以给对象定义一个变量key
  let process = {env: {}};

  const ENV = process.env.JSBIN_ENV || "development";
  const conf = {
    [ENV]: true
  };

  console.log([conf.development, conf.production]);


  //ES5中只能这样实现：
  var ENV = process.env.JSBIN_ENV || "development";
  var conf = {};
  conf[ENV] = true; 
  console.log([conf.development, conf.production]);
}

Console

["akira", "12-29"]
[true, undefined]

javscript

let point = {
  x : 100,
  y : 100,
  getLength : function(){
    let {x, y} = this;
    return Math.sqrt(x * x + y * y);
  }
}

console.log(point.getLength());

//用 for...in 遍历
for(let key in point){
  console.log([key, point[key]]);
}

//用 Object.keys 遍历
Object.keys(point).forEach((key) => console.log([key, point[key]]));

Console

141.4213562373095
["x", 100]
["y", 100]
["getLength", function(){
  let {x, y} = this;
  return Math.sqrt(x * x + y * y);
}]
["x", 100]
["y", 100]
["getLength", function(){
  let {x, y} = this;
  return Math.sqrt(x * x + y * y);
}]

值类型与引用类型

基本类型对应的包装类型

对象的拷贝

let x = 20, y = 30;

function foo(a, b){
  a++;
  b++;
  console.log([a, b]);
}

foo(x, y);

console.log([x, y]);
// 注意：Number是值类型，当把x，y作为参数传递给function的时候，只是传递了x,y的副本，所以执行完foo(x,y), x,y的值并没有变化。

const obj = {x: 20, y: 30};

function foo2(obj){
  obj.x++;
  obj.y++;
  console.log(obj);
}

foo2(obj);

console.log(obj);
// 注意：Object是引用类型，它是将obj里的引用自加，所以函数执行完，obj里的值会发生变化。

Console

[21, 31]
[20, 30]
[object Object] {
  x: 21,
  y: 31
}
[object Object] {
  x: 21,
  y: 31
}

var str = "Hello World";
var strObj = new String(str);
// 注释：如果写new是包装类型，如果不写new是值类型

console.log([str, strObj]); 
// console: ["Hello World", "Hello World"]

console.log([typeof str, typeof strObj]);
// console: ["string", "object"]

console.log([str instanceof String, strObj instanceof String]);
// console: [false, true]

var n = new Number(10);
console.log([typeof n, typeof ++n]);
// console: ["object", "number"]

console.log(Object.prototype.toString.call(10));
// console: [object Number]

let conf = {
  adapter: "sqlite",
  db: {
    sqlite: {
      name: "xxx.sqlite"
    },
    mysql: {
      name: "xxx",
      username: "work",
      passwd: "******"
    }
  }
};

//直接引用
let conf2 = conf;
conf2.adapter = "mysql";

console.log(conf.adapter);
// console: "mysql"

//ES5 浅拷贝
conf.adapter = "sqlite";
let copied = Object.assign({}, conf);
copied.adapter = "mysql";

console.log(conf.adapter);
// console: "sqlite"
console.log(copied.adapter);
// console: "mysql"
copied.db.sqlite.name = "yyy.sqlite";
console.log(conf.db.sqlite.name);
// console: "yyy.sqlite"

//深拷贝
function deepCopy(des, src){
  for(var key in src){
    let prop = src[key];
    if(typeof prop === "object"){
      des[key] = des[key] || {};
      deepCopy(des[key], prop);
    }else{
      des[key] = src[key];
    }
  }
  return des;
}

let deepCopied = deepCopy({}, conf);
deepCopied.db.sqlite.name = "zzz.sqlite";

console.log([deepCopied.db.sqlite.name, conf.db.sqlite.name]);
// console: ["zzz.sqlite", "yyy.sqlite"]

new 和 constructor

prototype

instanceOf

ES6 class

//假设 JS 没有 "new" 操作符，我们该如何实现创建对象？
function defineClass(initializer, proto){  
  return function f(...args){
    let obj = Object.create(proto);
    //f.prototype = proto; //just let instanceof make sense    
    obj.constructor = initializer;
    obj.constructor(...args);
    return obj;
  }
}

var Point = defineClass(function(x, y){
  this.x = x;
  this.y = y;
}, {
  getLength: function(){
    let {x, y} = this;
    return Math.sqrt(x * x + y * y);
  }
});

var p = Point(3, 4);
console.log([p.getLength(), p instanceof Point, p instanceof Object]);

//所以 "new" 其实是一种语法糖

// __proto__ 暴力构建原型链
var a = {x : 1}, 
    b = {y : 2}, 
    c = {z : 3};
    
b.__proto__ = a;
c.__proto__ = b;

console.log(c);

/**
 * console:
 * [object Object] {
 *   x: 1,
 *   y: 2,
 *   z: 3
 * }
 */

//使用 Object.create 构建原型链
var a = {x : 1};
var b = Object.create(a); // b继承对象a
b.y = 2;
var c = Object.create(b); // c继承对象b
c.z = 3;

console.log(c);
/**
 * console:
 * [object Object] {
 *   x: 1,
 *   y: 2,
 *   z: 3
 * }
 */

//使用构造器方式
function A() {
  this.x = 1;
}

function B() {
  this.y = 2;
}
B.prototype = new A();

function C() {
  this.z = 3;
}
C.prototype = new B();

var c = new C();
console.log(c);
/**
 * console:
 * [object Object] {
 *   x: 1,
 *   y: 2,
 *   z: 3
 * }
*/

设计原型链是为了代码复用,但是原型链有额外构造器调用的问题。

javascript

//原型继承
/**
 * abstract point
 */
function Point(components){
  console.log("Point constructor called");
  this.components = components;
}

Point.prototype = {
  getDimension: function(){
    return this.components.length;
  },
  getLength: function(){
    var sum = 0, components = this.components;
    for(var i = 0; i < components.length; i++){
      sum += Math.pow(components[i], 2);
    }
    return Math.sqrt(sum);
  }
};

function Point2D(x, y){
  Point.call(this, [x, y]);
}

Point2D.prototype = new Point();

Point2D.prototype.getXY = function(){
  var components = this.components;
  return {
    x: components[0],
    y: components[1]
  };
}

Console

"Point constructor called"
"Point constructor called"
["(3,4)", 5, true]
// 注意：这里调用了两次构造器

//原型继承
/**
 * abstract point
 */
function Point(dimension){
  console.log("Point constructor called");
  this.dimension = dimension;
}

Point.prototype = {
  setComponents: function(){
    components = [].slice.call(arguments);
    if(this.dimension !== components.length){
      throw new Error("Dimension not match!");
    }
    this.components = components;
  },
  getDimension: function(){
    return this.dimension;
  },
  getLength: function(){
    var sum = 0, components = this.components;
    for(var i = 0; i < components.length; i++){
      sum += Math.pow(components[i], 2);
    }
    return Math.sqrt(sum);
  }
};

function Point2D(x, y){
  this.setComponents(x, y);
}

Point2D.prototype = new Point(2);

Point2D.prototype.getXY = function(){
  var components = this.components;
  return {
    x: components[0],
    y: components[1]
  };
}

Point2D.prototype.toString = function(){
  return "(" + this.components + ")";
}

var p = new Point2D(3, 4);

console.log([p+"", p.getLength(), p instanceof Point]);

Console

"Point constructor called"
["(3,4)", 5, true]

注释：但这并不总是好的，尤其是在多重继承的时候

//原型继承
/**
 * abstract point
 */
function Point(components){
  console.log("Point constructor called");
  this.components = components;
}

Point.prototype = {
  getDimension: function(){
    return this.components.length;
  },
  getLength: function(){
    var sum = 0, components = this.components;
    for(var i = 0; i < components.length; i++){
      sum += Math.pow(components[i], 2);
    }
    return Math.sqrt(sum);
  }
};

function Point2D(x, y){
  Point.call(this, [x, y]);
}

Point2D.prototype = Object.create(Point.prototype);
//function PointT(){};
//PointT.prototype = Point.prototype;
//Point2D.prototype = new PointT();

Point2D.prototype.getXY = function(){
  var components = this.components;
  return {
    x: components[0],
    y: components[1]
  };
}

Point2D.prototype.toString = function(){
  return "(" + this.components + ")";
}

var p = new Point2D(3, 4);

console.log([p+"", p.getLength(), p instanceof Point]);

Console

"Point constructor called"
["(3,4)", 5, true]

Object

Function

Array

Date

Regex

Error

Math

ArrayBuffer

Promise

DataView

Map

Set

TypedArray // Uint16Array(buffer) Uint8Array(buffer)

Proxy（ES6）// 处理异步

Array.prototype.remove = function(item) {
  var idx = this.indexOf(item);
  if(idx >= 0){
    return this.splice(idx, 1)[0];
  }
  return null;
}

var arr = [1, 2, 3];
arr.remove(2);  //perfect??
console.log(arr);

for(var i in arr){
  if(!Number.isNaN(i-0)){
    console.log(i + ":" + arr[i]);
  }else{
    console.log(i + "是什么鬼？");
  }
}

/**
 * [1, 3]
 * "0:1"
 * "1:3"
 * "remove是什么鬼？"
 */
 
 // 注释：利用for in遍历数组或对象的好处是可以把值为undefined的过滤掉，它会把数组上可枚举的属性都遍历出来。

使用 ES5 新特性 defineProperty

规定禁止使用 for...in 操作数组，只用 for 或 Array.prototype.forEach

规定禁止往数组上随便添加方法

示例：

Object.defineProperty(Array.prototype, "remove", {
  value : function(item) {
    var idx = this.indexOf(item);
    if(idx >= 0) {
      return this.splice(idx, 1); 
    }
    return null;  
  },
  // enumerable: true 
  // 当且仅当该属性的enumerable为true时，该属性才能够出现在对象的枚举属性中。默认为 false。
});

var arr = [1, 2, 3];
arr.remove(2);
console.log(arr);

for(var i in arr) {
  if(!Number.isNaN(i-0)) {
    console.log(i + ":" + arr[i]);
  }else{
    console.log(i + "是什么鬼？");
  }
}

/** 
 * console:
 * [1, 3]
 * "0:1"
 * "1:3"
 */

function Point2D(x, y){
  this.x = x;
  this.y = y;
}

Object.defineProperty(Point2D.prototype, "length", {
  get: function() {
    let {x, y} = this;
    return Math.sqrt(x * x + y * y);
  },
  set: function(len) {
    let arc = Math.atan2(this.y, this.x);
    this.x = len * Math.cos(arc);
    this.y = len * Math.sin(arc);
  }
});

Object.defineProperty(Point2D.prototype, "arc", {
  get: function(){
    let {x, y} = this;
    return 180 * Math.atan2(y, x) / Math.PI;
  },
  set: function(arc){
    arc = Math.PI * arc / 180;
    let len = this.length;
    this.x = len * Math.cos(arc);
    this.y = len * Math.sin(arc);
  }
});

let p = new Point2D(1, 1);

console.log([p.length, p.arc]);
// [1.4142135623730951, 45]

p.length *= 2;

console.log([p.x, p.y]);
// [2.0000000000000004, 2]

p.arc = 90;
console.log([p.x, p.y]);
// [1.7319121124709868e-16, 2.8284271247461903]

const view = {
  nameEl: document.getElementById("name"),
  ageEl: document.getElementById("age"),
  submitBtn: document.getElementById("confirm")
}

view.submitBtn.addEventListener("click", function(evt){
  console.log("你要提交的数据是：" + [user.name, user.age]);
  evt.preventDefault();
});

function User(name, age){
  this.name = name;
  this.age = age;
}

User.prototype.bind = function(view){
  view.nameEl.addEventListener("change", evt => {
     this.name = evt.target.value;
  });
  view.ageEl.addEventListener("change", evt => {
     this.age = evt.target.value;
  });
}

Object.defineProperty(User.prototype, "name", {
  set: function(name){
    view.nameEl.value = name;
  },
  get: function(){
    return view.nameEl.value;
  }
});

Object.defineProperty(User.prototype, "age", {
  set: function(name){
    var ageOptions = Array.from(view.ageEl.options)
              .map(item => item.innerHTML);
    if(ageOptions.indexOf(name) === "-1"){
      throw new Error("无效的年龄格式");
    }
    view.ageEl.value = name;
  },
  get: function(){
    return view.ageEl.value;
  }
});

var user = new User("akira", "80后");
user.bind(view);

演示 demo

文章内容来源：360奇舞团前端星课程。

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