前端 js 基础对象（3）

js 对象定义

<!DOCTYPE html>
<html>
<body><h1>JavaScript 对象创建</h1><p id="demo1"></p>=======================
<p>new</p>
<p id="demo"></p><script>
// 创建对象：
var persona = {firstName : "Bill",lastName  : "Gates",age       : 62,eyeColor  : "blue"
};// 显示对象中的数据：
document.getElementById("demo1").innerHTML =
persona.firstName + " 已经 " + persona.age + " 岁了。";//==========================var person = new Object();
person.firstName = "Bill";
person.lastName = "Gates";
person.age = 50;
person.eyeColor = "blue"; document.getElementById("demo").innerHTML =
person.firstName + " is " + person.age + " years old.";</script></body>
</html>

js 对象属性

<!DOCTYPE html>
<html>
<body><h1>JavaScript 对象属性</h1><p>访问对象属性有两种不同的方法：</p><p>您可以使用 .property 或 ["property"]。</p><p id="demo"></p>
//======================
<p id="demo1"></p><script>
var person = {firstname:"Bill",lastname:"Gates",age:62,eyecolor:"blue"
};
person.nationality = "English";  //添加数据delete person.age; //删除 age数据
//======================
document.getElementById("demo").innerHTML = person["firstname"] + " is " + person["age"] + " years old.";//======================document.getElementById("demo1").innerHTML =  " I like  " +person.eyecolor  +" My name "+ person.lastname ;
</script></body>
</html>

js 对象方法

<!DOCTYPE html>
<html>
<body><p id="demo"></p><script>
var person = {firstName: "Bill",lastName : "Gates",id     : 678,
};
person.name = function() {return this.firstName + " " + this.lastName;
};document.getElementById("demo").innerHTML =
"My friend is " + person.name(); 
</script></body>
</html>

js 对象显示

<!DOCTYPE html>
<html>
<body><h1>JavaScript 对象</h1><p>显示对象属性：</p>
<p id="demo1"></p><p id="demo"></p><script>
const person = {name: "Bill",age: 19,city: "Seattle"
};
document.getElementById("demo1").innerHTML = person;
document.getElementById("demo").innerHTML = person.name + ", " + person.age + ", " + person.city;
</script></body>
</html>

js set get 对象访问

<!DOCTYPE html>
<html>
<body><h1>JavaScript Getter 和 Setter</h1><p>Getter 和 Setter 允许您通过方法获取和设置属性。</p><p>此示例使用 lang 属性设置语言属性的值。</p>========== set ==========
<p id="demo"></p>========== get ==========
<p id="demo1"></p><script>//========== set ==========
// Create an object:
var person = {firstName: "Bill",lastName : "Gates",language : "en",set lang(value) {this.language = value;}
};
// 使用 set 设置属性：
person.lang = "zh";
// 显示对象的数据：
document.getElementById("demo").innerHTML = person.language;// ========== get ==========
// 创建对象：
var person1 = {firstName: "Bill",lastName : "Gates",language : "en",get lang1() {return this.language;}
};
// 使用 getter 显示来自对象的数据：
document.getElementById("demo1").innerHTML = person1.lang1;
</script></body>
</html>

js 对象构造器

<!DOCTYPE html>
<html>
<body><h1>JavaScript 对象构造器</h1><p id="demo"></p>
//====================<p id="demo1"></p>
<script>
// Person 对象的构造器函数
function Person(firstName,lastName,age,eyeColor) {this.firstName = firstName;this.lastName = lastName;this.age = age;this.eyeColor = eyeColor;this.changeName = function (name) {this.lastName = name;}
}
// 创建 Person 对象
var myFriend = new Person("Bill","Gates",62,"green");// 修改姓氏
myFriend.changeName("Jobs");// 显示姓氏
document.getElementById("demo").innerHTML =
"My friend's last name is " + myFriend.lastName;//====================// Person 对象的构造器函数
function Person1(first, last, age, eye) {this.firstName = first;this.lastName = last;this.age = age;this.eyeColor = eye;
}// 创建两个 Person 对象
var myFriend1 = new Person1("Bill", "Gates", 62, "blue");
var myBrother1 = new Person1("Steve", "Jobs", 56, "green");// 向第一个对象添加 name 方法
myFriend1.name = function() {return this.firstName + " " + this.lastName;
};// 显示全名
document.getElementById("demo1").innerHTML =
"My friend is " + myFriend1.name(); 
</script></body>
</html>

js 可迭代对象

可迭代对象（Iterables）是可以使用 for..of 进行迭代的对象。

从技术上讲，可迭代对象必须实现 Symbol.iterator 方法。

<!DOCTYPE html>
<html>
<body><h1>JavaScript 可迭代对象</h1><p>迭代字符串：</p><p id="demo"></p>
========================<p>遍历数组：</p><p id="demo1"></p><script>
// 创建字符串
const name = "W3School";// 列出所有元素
let text = ""
for (const x of name) {text += x + "<br>";
}document.getElementById("demo").innerHTML = text;//=================
// 创建数组
const letters = ["a","b","c"];// 列出所有元素
let text1 = "";
for (const x of letters) {text1 += x + "<br>";
}document.getElementById("demo1").innerHTML = text1;
</script>
</body>
</html>

自制迭代器

参考JavaScript 可迭代对象 (w3school.com.cn)

<!DOCTYPE html>
<html>
<body>
<h1>JavaScript 可迭代对象</h1><p>自制的可迭代对象：</p><p id="demo"></p><script>
// 自制的可迭代对象
function myNumbers() {let n = 0;return {next: function() {n += 10;return {value:n, done:false};}};
}//n.next 是向下执行一共执行了三次 返回状态是true
// 三次执行之后 第四次就变成了false // 创建可迭代对象
const n = myNumbers();
n.next(); // 10
n.next(); // 20
n.next(); // 30document.getElementById("demo").innerHTML = n.next().value;
</script>
</body>
</html>

js map

Map.size

size 属性返回 Map 中元素的数量：

<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Map 对象</h1>
<p>使用 Map.set()：</p><p id="demo"></p>
====================
// 创建 Map
<p id="demo1"></p>==========
删除 size 属性返回 Map 中元素的数量：
<p id="demo2"></p><script>
// 创建 Map
const fruits = new Map();// 设置 Map 的值
fruits.set("apples", 500);
fruits.set("bananas", 300);
fruits.set("oranges", 200);document.getElementById("demo").innerHTML = fruits.get("apples");
//=========================
// 创建 Map
const fruits1 = new Map([["apples", 500],["bananas", 300],["oranges", 200]
]);document.getElementById("demo1").innerHTML = fruits1.get("apples");
//=======================
// 创建 Map
const fruits2 = new Map([["apples", 500],["bananas", 300],["oranges", 200]
]);// Delete an Element
fruits2.delete("apples");document.getElementById("demo2").innerHTML = fruits2.size;</script></body>
</html>

js call

call() 方法是预定义的 JavaScript 方法。

它可以用来调用所有者对象作为参数的方法。

通过 call()，您能够使用属于另一个对象的方法。

本例调用 person 的 fullName 方法，并用于 person1：

<!DOCTYPE html>
<html>
<body><h1>JavaScript 函数</h1><p>此例调用 person 的 fullName 方法，在 person1 上使用它：</p><p id="demo"></p><script>
var person = {fullName: function(city, country) {return this.firstName + " " + this.lastName + "," + city + "," + country;}
}
var person1 = {firstName:"Bill",lastName: "Gates"
}
var person2 = {firstName:"Steve",lastName: "Jobs"
}
var x = person.fullName.call(person1, "Seatle", "USA"); 
document.getElementById("demo").innerHTML = x; 
</script></body>
</html>

js apply

参考 JavaScript 函数 Apply (w3school.com.cn)

JavaScript apply() 方法

apply() 方法与 call() 方法非常相似

<!DOCTYPE html>
<html>
<body><h1>JavaScript 函数</h1><p>在此示例中，person 的 fulllName 方法在 person1 上<b>应用</b>：</p><p id="demo"></p><script>
var person = {fullName: function(city, country) {return this.firstName + " " + this.lastName + "," + city + "," + country;}
}
var person1 = {firstName:"Bill",lastName: "Gates"
}
var x = person.fullName.apply(person1, ["Seatle", "USA"]); 
document.getElementById("demo").innerHTML = x; 
</script></body>
</html>

js 闭包

<!DOCTYPE html>
<html>
<body><h1>JavaScript 闭包</h1><p>使用局部变量计数。</p><button type="button" onclick="myFunction()">计数！</button><p id="demo">0</p><script>
var add = (function () {var counter = 0;return function () {counter += 1; return counter;}
})();function myFunction(){document.getElementById("demo").innerHTML = add();
}
</script></body>
</html>

js 类继承

参考 JavaScript 类继承 (w3school.com.cn)

super() 方法引用父类。

通过在 constructor 方法中调用 super() 方法，我们调用了父级的 constructor 方法，获得了父级的属性和方法的访问权限。

<!DOCTYPE html>
<html>
<body><h1>JavaScript Class 继承</h1><p>请使用 "extends" 关键字从另一个类继承所有方法。</p>
<p>使用 "super" 方法调用父级的构造函数。</p><p id="demo"></p><script>
class Car {constructor(brand) {this.carname = brand;}present() {return 'I have a ' + this.carname;}
}class Model extends Car {constructor(brand, mod) {super(brand);this.model = mod;}show() {return this.present() + ', it is a ' + this.model;}
}let myCar = new Model("Ford", "Mustang");
document.getElementById("demo").innerHTML = myCar.show();
</script></body>
</html>