JavaScript 中的继承
那些定义在构造器函数中的、用于给予对象实例的。这些都很容易发现 - 在您自己的代码中，它们是构造函数中使用this.x = x类型的行；在内置的浏览器代码中，它们是可用于对象实例的成员（通常通过使用new关键字调用构造函数来创建，例如var myInstance = new myConstructor()）。
那些直接在构造函数上定义、仅在构造函数上可用的。这些通常仅在内置的浏览器对象中可用，并通过被直接链接到构造函数而不是实例来识别。 例如Object.keys()。
那些在构造函数原型上定义、由所有实例和对象类继承的。这些包括在构造函数的原型属性上定义的任何成员，如myConstructor.prototype.x()。
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Object-oriented JavaScript inheritance</title>
</head>
<body>
<div>
<label for="jscode">Enter code:</label>
<input type="text" id="jscode">
<button>Submit code</button>
</div>
<p></p>
</body>
<script>
const input = document.querySelector('input');
const btn = document.querySelector('button');
const para = document.querySelector('p');
btn.onclick = function() {
const code = input.value;
para.textContent = eval(code);
}
// 定义 Person 构造函数
function Person(first, last, age, gender, interests) {
this.name = {
first,
last
};
this.age = age;
this.gender = gender;
this.interests = interests;
};
//Person 添加 bio 方法
Person.prototype.bio = function() {
// First define a string, and make it equal to the part of
// the bio that we know will always be the same.
let string = this.name.first + ' ' + this.name.last + ' is ' + this.age + ' years old. ';
// define a variable that will contain the pronoun part of
// the second sentence
let pronoun;
// check what the value of gender is, and set pronoun
// to an appropriate value in each case
if(this.gender === 'male' || this.gender === 'Male' || this.gender === 'm' || this.gender === 'M') {
pronoun = 'He likes ';
} else if(this.gender === 'female' || this.gender === 'Female' || this.gender === 'f' || this.gender === 'F') {
pronoun = 'She likes ';
} else {
pronoun = 'They like ';
}
// add the pronoun string on to the end of the main string
string += pronoun;
// use another conditional to structure the last part of the
// second sentence depending on whether the number of interests
// is 1, 2, or 3
if(this.interests.length === 1) {
string += this.interests[0] + '.';
} else if(this.interests.length === 2) {
string += this.interests[0] + ' and ' + this.interests[1] + '.';
} else {
// if there are more than 2 interests, we loop through them
// all, adding each one to the main string followed by a comma,
// except for the last one, which needs an and & a full stop
for(let i = 0; i < this.interests.length; i++) {
if(i === this.interests.length - 1) {
string += 'and ' + this.interests[i] + '.';
} else {
string += this.interests[i] + ', ';
}
}
}
// finally, with the string built, we alert() it
alert(string);
};
//Person greeting 方法
Person.prototype.greeting = function() {
alert('Hi! I\'m ' + this.name.first + '.');
};
Person.prototype.farewell = function() {
alert(this.name.first + ' has left the building. Bye for now!');
}
//创建 Person 的实例对象
let person1 = new Person('Tammi', 'Smith', 17, 'female', ['music', 'skiing', 'kickboxing']);
//定义 Teacher 的构造函数
function Teacher(first, last, age, gender, interests, subject) {
//peeson.call 继承 person 的属性和方法
Person.call(this, first, last, age, gender, interests);
//额外的 subject 属性
this.subject = subject;
}
//设置 Teacher() 的原型和构造器引用
Teacher.prototype = Object.create(Person.prototype);
Teacher.prototype.constructor = Teacher;
//添加 Teacher 的greeting 的方法
Teacher.prototype.greeting = function() {
var prefix;
if(this.gender === 'male' || this.gender === 'Male' || this.gender === 'm' || this.gender === 'M') {
prefix = 'Mr.';
} else if(this.gender === 'female' || this.gender === 'Female' || this.gender === 'f' || this.gender === 'F') {
prefix = 'Mrs.';
} else {
prefix = 'Mx.';
}
alert('Hello. My name is ' + prefix + ' ' + this.name.last + ', and I teach ' + this.subject + '.');
};
var teacher1 = new Teacher('Dave', 'Griffiths', 31, 'male', ['football', 'cookery'], 'mathematics');
</script>
</html>
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