Question

初始化javascript对象时，我想从函数执行中获取属性值。

到那时，我的对象看起来像这样：

request.resource.data.status == "new" || "viewed";

很明显，每次调用request.resource.data.status == "new" || request.resource.data.status == "viewed";时，var objectName = function(){} objectName.prototype.initialize = function() { this.attribute = functionOne(); functionOne() { return httpRequest(); } }都会被执行，并且因为它是异步函数，结果是instance.attribute。我知道我需要getter和setter方法来实现这一点，但是这样做的正确方法是保持这个原型结构。

我尝试了以下

functionOne

但是当我拨打undefined时，我收到了此错误：

objectName.prototype.initialize = function() {
  this.attribute = undefined;
  Object.defineProperty(this, "attribute", {
    get: function() { return this.attribute },
    set: functionOne()
  });
}

Answer 1

const objectName = function(){}

const objectName.prototype.initialize = function() {
  this.attribute = undefined;
  Object.defineProperty(this, "attribute", {
    get: function() { return this.attribute },
    set: functionOne()
  });
}

const instance = new objectOne()

// This is infinitely recursive
instance.attribute 
// because instance.attribute invokes attribute getter, which returns instance.attribute
// which invokes attribute getter, which returns instance.attribute, which invokes ......
// which "eventually" (actually within a few microseconds) overflows the stack

var objectName = function(){}

objectName.prototype.initialize = function() {
  // Function called immediately when you initialize. Result is
  // essentially cached to this.attribute.
  this.attribute = functionOne();

  // returns whatever httpRequest returns
  function functionOne() {
    return httpRequest();
  }
}

由于httpRequest显然是异步的，因此基本上有两种类型的回报：

新的或维护良好的模块可能会提供promise API，在这种情况下，您可以在返回的承诺上调用.then。

instance.attribute.then(function(attr) {
  doSomethingWithAttribute(attr)
})

// or 

(async function() {
  const attr = await instance.attribute
  doSomethingWithAttribute(attr)
})()

较旧的模块可能会使用回调系统。所以你需要立即传递一个功能。

var objectName = function(){}

objectName.prototype.initialize = function() {
  // Notice I removed the parens here, this is no longer just about
  // immediate invocation. We need a callback to give to httpRequest.
  // so now attribute is basically an alias for functionOne. You could
  // instead accept a callback to attribute and pass it on to functionOne.
  this.attribute = functionOne;

  functionOne(callback) {
    return httpRequest(callback);
  }
}

// Just for reference, but not relevant to the question, this is a more concise
// version of the function above assigned to objectName.prototype.initialize.
const equivalentInitialize = {
  this.attribute = function(callback) {
    return httpRequest(callback);
  };
}

const instance = new objectOne()
instance.attribute(doSomethingWithAttribute)

为了使其更具可组合性，您可以将回调API包装在promise中。

var objectName = function(){}

objectName.prototype.initialize = function() {
  this.attribute = new Promise(resolve => {
    httpRequest(resolve)
  })
}

const instance = new objectName()
instance.atttribute
  .then(doSomethingWithAttribute)

更好的是，你可以忘记所有这些getter和setter废话，这在Javascript中甚至没有提供你认为它的安全性。

// Making some wild guesses about api here, since I don't what you are using 
// here to make a request

httpRequest({ url, method, apiKey })
  .then(doSomethingWithResponse)

Javascript setter和getter over prototype initialization function

1 个答案: