Javascript 如何调用父构造函数？
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how to call parent constructor?
提问by Moon
Let's say I have the following code snippet.
假设我有以下代码片段。
function test(id) { alert(id); }
testChild.prototype = new test();
function testChild(){}
var instance = new testChild('hi');
Is it possible to get alert('hi')? I get undefinednow.
有可能得到alert('hi')吗？我undefined现在明白了。
采纳答案by Anton Strogonoff
That's how you do this in CoffeeScript:
这就是你在 CoffeeScript 中的做法：
class Test
constructor: (id) -> alert(id)
class TestChild extends Test
instance = new TestChild('hi')
Nope, I'm not starting a holy war. Instead, I'm suggesting to take a look at resulting JavaScript code to see how subclassing could be implemented:
不，我不会发动圣战。相反，我建议查看生成的 JavaScript 代码，以了解如何实现子类化：
// Function that does subclassing
var __extends = function(child, parent) {
for (var key in parent) {
if (Object.prototype.hasOwnProperty.call(parent, key)) {
child[key] = parent[key];
}
}
function ctor() { this.constructor = child; }
ctor.prototype = parent.prototype;
child.prototype = new ctor;
child.__super__ = parent.prototype;
return child;
};
// Our code
var Test, TestChild, instance;
Test = function(id) { alert(id); };
TestChild = function() {
TestChild.__super__.constructor.apply(this, arguments);
}; __extends(TestChild, Test);
instance = new TestChild('hi');
// And we get an alert
See it in action at http://jsfiddle.net/NGLMW/3/.
在http://jsfiddle.net/NGLMW/3/ 上查看它的实际效果。
To stay correct, the code is slightly modified and commented to be more readable, compared to CoffeeScript output.
为保持正确，与 CoffeeScript 输出相比，代码稍作修改和注释以提高可读性。
回答by roylaurie
JS OOP ...
JS面向对象...
// parent class
var Test = function(id) {
console.log(id);
};
// child class
var TestChild = function(id) {
Test.call(this, id); // call parent constructor
};
// extend from parent class prototype
TestChild.prototype = Object.create(Test.prototype); // keeps the proto clean
TestChild.prototype.constructor = TestChild; // repair the inherited constructor
// end-use
var instance = new TestChild('foo');
回答by Sk606
You already have many answers, but I'll throw in the ES6 way, which IMHO is the new standard way to do this.
您已经有很多答案，但我会采用 ES6 方式，恕我直言，这是执行此操作的新标准方式。
class Parent {
constructor() { alert('hi'); }
}
class Child extends Parent {
// Optionally include a constructor definition here. Leaving it
// out means the parent constructor is automatically invoked.
constructor() {
// imagine doing some custom stuff for this derived class
super(); // explicitly call parent constructor.
}
}
// Instantiate one:
var foo = new Child(); // alert: hi
回答by JCotton
By taking advantage of variable argumentsand the apply()method, you could do it this way. Here's a fiddlefor this example.
通过利用可变参数和apply()方法，您可以这样做。这是此示例的小提琴。
function test(id) { alert(id); }
function testChild() {
testChild.prototype.apply(this, arguments);
alert('also doing my own stuff');
}
testChild.prototype = test;
var instance = new testChild('hi', 'unused', 'optional', 'args');
回答by Paul Sonier
You need to declare the function testChild()before you set its prototype. Then you need to call testChild.testto call the method. I believe you want to set testChild.prototype.test = test, then you can call testChild.test('hi')and it should resolve properly.
您需要function testChild()在设置其原型之前声明。然后你需要调用testChild.test来调用方法。我相信你想设置testChild.prototype.test = test，然后你可以打电话testChild.test('hi')，它应该能正确解决。
