Typescript中class的extends码源分析

学习typescript的乐趣在于看它的码源是如何要js实现的、

今天要分析的是类继承的码源。我们先来看一下使用ES5的组合继承是如何做到的：

function Person(name) {
    this.name = name;
}
Person.prototype.sayName = function () {
    console.log(this.name);
};
function Student(name, school) {
    Person.call(this, name)
    this.school = school;
}
Student.prototype = Person.prototype;
Student.prototype.saySchool = function () {
    console.log(this.school);
};
let student = new Student('wangting', 'NT');
console.log('school' in student);
console.log('saySchool' in student);
console.log('name' in student);
console.log('sayName' in student);

再来看一下typescript的实现：

var __extends = (this && this.__extends) || (function () {
    var extendStatics = 
        Object.setPrototypeOf ||
        ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
        function (d, b) { for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p]; };
    return function (d, b) {
        // 类属性和类方法的继承
        extendStatics(d, b);

        function __() { this.constructor = d; }
        // d的原型对象
        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
    };
})();
var Person = (function () {
    function Person(name) {
        this.name = name;
    }
    Person.prototype.sayName = function () {
        console.log(this.name);
    };
    Person.Country = 'China';
    return Person;
}());
var Student = (function (_super) {
    __extends(Student, _super);
    function Student(name, school) {
        var _this = _super.call(this, name) || this;
        _this.school = school;
        return _this;
    }
    Student.prototype.saySchool = function () {
        console.log(this.school);
    };
    return Student;
}(Person));
var student = new Student('wangting', 'NT');
console.log(Student.Country); // China
student.saySchool(); // NT
student.sayName(); // wangting