如何调用父构造函数？ [英] how to call parent constructor?

问题描述

假设我有以下代码段。

function test(id) { alert(id); }

testChild.prototype = new test();

function testChild(){}

var instance = new testChild('hi');

是否可以获得 alert（'hi'）？我现在得到 undefined 。

Is it possible to get alert('hi')? I get undefined now.

推荐答案

这就是你在CoffeeScript中这样做的方法：

That's how you do this in CoffeeScript:

class Test
  constructor: (id) -> alert(id)

class TestChild extends Test

instance = new TestChild('hi')

不，我没有开始圣战。相反，我建议看看生成的JavaScript代码，看看如何实现子类化：

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:

// 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

在< a href =http://jsfiddle.net/NGLMW/3/ =noreferrer> http://jsfiddle.net/NGLMW/3/ 。

为了保持正确，与CoffeeScript输出相比，代码稍作修改并注释为更具可读性。

To stay correct, the code is slightly modified and commented to be more readable, compared to CoffeeScript output.

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