仅仅模拟多重继承是混合使用的唯一优势吗:
Object.assign( MyClassA.prototype, MyMixinB )
继承 vs. 组合
class MyClass extends MyClassB {
// MyClassB = class version of MyMixinB
在ES6 JavaScript中是什么? 谢谢。
仅仅模拟多重继承是混合使用的唯一优势吗:
Object.assign( MyClassA.prototype, MyMixinB )
继承 vs. 组合
class MyClass extends MyClassB {
// MyClassB = class version of MyMixinB
Object.assign(MyClassA.prototype, MyMixinB)
MyMixinB
作为基于对象的混入提供额外的行为,例如...
var arr = ['object', 'based', 'mixin', 'approach'];
var list = { length: 4, 0: 'the', 1: 'quick', 2: 'brown', 3: 'fox' };
console.log('(typeof arr.last) : ', (typeof arr.last));
console.log('(typeof list.last) : ', (typeof list.last));
const withObjectBasedListLastBehavior = {
last: function () {
return this[this.length - 1];
}
}
Object.assign(Array.prototype, withObjectBasedListLastBehavior);
Object.assign(list, withObjectBasedListLastBehavior);
console.log('(typeof arr.last) : ', (typeof arr.last));
console.log('arr.last() : ', arr.last());
console.log('(typeof list.last) : ', (typeof list.last));
console.log('list.last() : ', list.last());
console.log('(arr.last === list.last) : ', (arr.last === list.last));
console.log('(arr.last === Array.prototype.last) : ', (arr.last === Array.prototype.last));
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withObjectBasedListLastBehavior
mixin 为类似列表结构提供了通用实现的 last
方法。这个结构本身不会产生什么影响。通过 Object.assign
,可以将 last
列表行为分配给任何类似于列表的结构。但是,在第一个示例中,OP将mixin分配给了一个原型。因此,除非调用没有自己的 last
方法的实例,否则不会使用所获得的新行为。然后进行原型委派...现在的原型last
将在调用对象的上下文中被调用。call
和apply
方法。class MyClass extends MyClassB {
// MyClassB = class version of MyMixinB
... 并将其更改为类似于此类的东西 ...
const withFunctionBasedListLastBehavior = (function () {
function last() { // single implementation
return this[this.length - 1];
}
return function() { // always going to share the above
this.last = last; // single implementation, thus always
}; // featuring one and the same signature.
}());
const withFunctionBasedListFirstBehavior = (function () {
function first() {
return this[0];
}
return function() {
this.first = first;
};
}());
const withFunctionBasedListItemBehavior = (function () {
function item(idx) {
return this[idx];
}
return function() {
this.item = item;
};
}());
class ListWrapper {
constructor(list) {
// mixin in / explicit delegation
withFunctionBasedListFirstBehavior.call(list);
withFunctionBasedListLastBehavior.call(list);
withFunctionBasedListItemBehavior.call(list);
// forwarding
this.first = function() {
return list.first();
};
this.last = function() {
return list.last();
};
this.item = function(idx) {
return list.item(idx);
}
}
}
class Queue extends ListWrapper { // inheritance part I.
constructor() {
const list = [];
super(list); // inheritance part II.
// queue specific behavior
this.enqueue = function(value) {
list.push(value);
return value;
};
this.dequeue = function() {
return list.shift();
};
}
}
var queue = new Queue;
console.log("queue.enqueue('the') : ", queue.enqueue('the'));
console.log("queue.enqueue('quick') : ", queue.enqueue('quick'));
console.log("queue.enqueue('brown') : ", queue.enqueue('brown'));
console.log("queue.enqueue('fox') : ", queue.enqueue('fox'));
console.log("queue.first() : ", queue.first());
console.log("queue.last() : ", queue.last());
console.log("queue.item(2) : ", queue.item(2));
console.log("queue.dequeue() : ", queue.dequeue());
console.log("queue.dequeue() : ", queue.dequeue());
console.log("queue.dequeue() : ", queue.dequeue());
console.log("queue.first() : ", queue.first());
console.log("queue.last() : ", queue.last());
console.log("queue.item(2) : ", queue.item(2));
console.log("queue.dequeue() : ", queue.dequeue());
console.log("queue.dequeue() : ", queue.dequeue());
console.log('(queue instanceof Queue) : ', (queue instanceof Queue));
console.log('(queue instanceof ListWrapper) : ', (queue instanceof ListWrapper));
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