Question

我试图更好，更深入地了解JS，以提高自己的技能。因此，我编写了一个演示应用程序，该应用程序在加载HTML文档后添加了JS，CSS并创建了DOM元素。我还添加了异步/等待和承诺。当我等待承诺被解决时（JSFiddle代码中的第31行），该应用程序停止工作。

似乎我听不懂什么，但是我不知道确切地知道什么以及如何找到方向，什么以及如何改进。所以，我需要你的建议。

这是小提琴：

http://jsfiddle.net/k4z86nw3/9/

现在它可以了，但是，正如我已经提到的，如果您取消注释第31行，

(await wait)();

它将停止工作。

Answer 1

如https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise所示，它需要在promise中调用resolve函数。

'use strict';

function initAnimation() {
  (new WOW()).init();
}

function addCSS() {
  let cssStyleSheet = document.createElement('link');
  cssStyleSheet.rel = 'stylesheet';
  cssStyleSheet.href = 'https://cdnjs.cloudflare.com/ajax/libs/animate.css/3.7.0/animate.min.css';
  document.head.appendChild(cssStyleSheet);
}

async function addWOW() {
  let wowScriptJS = document.createElement('script');
  wowScriptJS.src = 'https://cdnjs.cloudflare.com/ajax/libs/wow/1.1.2/wow.min.js';
  wowScriptJS.onload = initAnimation;
  document.body.appendChild(wowScriptJS);
}

(async function run() {

  let res = await fetch('https://dl.dropboxusercontent.com/s/i6ckrkzscn6uuhq/data.json');

  addCSS();
  addWOW();

  let wait = new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log('Already waited N sec.');
      resolve();
    }, 1000);
  });

  await wait; // <<< === IF YOU UNCOMMENT THIS LINE, APP WILL STOP WORKING

  let jsonData = await res.json();
  let sections = jsonData.sections;

  function addNewChildToParentDOMElement({
    childDOMElementName,
    cssClasses,
    innerHTML,
    src,
    parentDOMNode
  }) {
    let childDOMElement = document.createElement(childDOMElementName);
    if (cssClasses) {
      childDOMElement.classList.add(...cssClasses);
    }
    if (innerHTML) {
      childDOMElement.innerHTML = innerHTML;
    }
    if (src) {
      childDOMElement.src = src;
    }
    parentDOMNode.appendChild(childDOMElement);
  }

  for (let i = 0; i < sections.length; i++) {
    console.warn('i==', i);
    let newDOMItem = document.createElement('div');

    addNewChildToParentDOMElement({
      childDOMElementName: 'h2',
      cssClasses: ['text-centered'],
      innerHTML: sections[i].title,
      parentDOMNode: newDOMItem
    });

    addNewChildToParentDOMElement({
      childDOMElementName: 'p',
      cssClasses: ['text-centered', 'wow', 'bounceInUp'],
      innerHTML: sections[i].desc,
      parentDOMNode: newDOMItem
    });


    let div = document.createElement('div');
    div.classList.add('img-centered');
    div.classList.add('wow');
    div.classList.add('flipInX');

    addNewChildToParentDOMElement({
      childDOMElementName: 'img',
      src: sections[i].imgURL,
      parentDOMNode: div
    });

    newDOMItem.appendChild(div);

    document.body.appendChild(newDOMItem);
  }

})();

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>aj_test</title>
  <style>
    .text-centered {
      text-align: center;
    }
    
    .img-centered {
      text-align: center;
    }
  </style>
</head>

<body>
</body>

</html>

Answer 2

您正在等待承诺解决（在Promise执行程序函数中调用resolve）。您应该像函数一样调用resolve（或reject）来解决（或在出错的情况下拒绝）您的诺言：

let wait = new Promise((resolve, reject) => {
  setTimeout(() => {
    const someFunc = () => console.log('Already waited N sec.');
    resolve(someFunc);
  }, 1000);
});

(await wait)(); // in this line you are waiting result of promise resolving and then calling returned someFunc

当使用带有promise和appendChild的async / await时，应用程序停止工作

2 个答案: