使用构造函数的 Javascript 继承

Question

我正在尝试使一个构造函数成为另一个构造函数的父函数。

function Fruit() {
    this.isEatable = function() {
        return eatable;
    };
}
function Apple(eatable , sweet) {
    this.isSweet = function() {
        return sweet;
    };
    var instance = {};
    Fruit.apply(instance);
    _.extend(this, instance);
}

var a = new Apple(true, false);

console.log(a.isEatable()); // Uncaught ReferenceError: eatable is not defined

但是正如你所看到的，我收到了一个错误，原因是什么？使一个函数继承另一个函数的更好方法是什么？

我也尝试了以下方法，但仍然遇到相同的错误:

function Fruit() {
    this.isEatable = function() {
        return eatable;
    };
}
function Apple(eatable , sweet) {
    this.isSweet = function() {
        return sweet;
    };
}

_.extend(Apple.prototype , Fruit.prototype);// I use lodash library
var a = new Apple(true, false);

console.log(a.isEatable()); // Uncaught ReferenceError: eatable is not defined

Answer 1

尝试以下操作

function Fruit(eatable) {
    this.eatable = eatable;
    this.isEatable = function() {
        return this.eatable;
    };
}

function Apple(eatable , sweet) {
    // Call the constructor of the inherited 'object'
    Fruit.call(this, eatable);

    this.sweet = sweet;

    this.isSweet = function() {
        return this.sweet;
    };
}

// Inherit the Fruit.prototype methods for Apple
Apple.prototype = Object.create(Fruit.prototype);

var a = new Apple(true, false);

console.log(a.isEatable());

这是基于 MDN Object.create 中作为示例给出的(非常有用)代码。文档。这是 JSFiddle .