怎样从零开始创建一个谷歌扩展程序？-蒲公英云

format_png

来源：Jimmy https://juejin.im/post/6890719051820695565

谷歌扩展程序是个HTML,CSS和JAVASCRIPT应用程序，它可以安装在谷歌浏览器上。

下面的内容，指导感兴趣的人儿创建一个谷歌扩展程序，它允许我们去获取不同国家新型冠状病毒肺炎-covid19案例的信息。

format_png 1 extension

步骤1：创建目录

创建一个名为dist的文件夹，然后创建以下的文件。

format_png 2 step1

步骤2：创建HTML文件

如下内容：

<!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>Covid 19</title>
    <link rel="stylesheet" href="./style.css" />
    <script src="https://unpkg.com/axios/dist/axios.min.js"></script>
    <script type="text/javascript" src="index.js" defer></script>
  </head>
  <body>
    <div class="header">Covid 19</div>
    <div class="container">
    <form class="form-data" autocomplete="on">
      <div class="enter-country">
        <b>Enter a country name:</b>
      </div>
      <div>
        <input type="text" class="country-name" />
      </div><br>
      <button class="search-btn">Search</button>
    </form>
    <div class="result">
      <div class="loading">loading...</div>
      <div class="errors"></div>
      <div class="data"></div>
      <div class="result-container">
        <p><strong>New cases: </strong><span class="todayCases"></span></p>
        <p><strong>New deaths: </strong><span class="todayDeaths"></span></p>
        <p><strong>Total cases: </strong><span class="cases"></span></p>
        <p><strong>Total recovered: </strong> <span class="recovered"></span></p>
        <p><strong>Total deaths: </strong><span class="deaths"></span></p>
        <p><strong>Total tests: </strong><span class="tests"></span></p>
        <center><span class="safe">Stay Safe and Healthy</span></center>
      </div>
    </div>
  </div>
</body>
</html>

步骤3：创建JAVASCRIPT文件

JAVASCRIPT文件用来处理API，内容如下：

const api = "https://coronavirus-19-api.herokuapp.com/countries";
const errors = document.querySelector(".errors");
const loading = document.querySelector(".loading");
const cases = document.querySelector(".cases");
const recovered = document.querySelector(".recovered");
const deaths = document.querySelector(".deaths");
const tests=document.querySelector(".tests");
const todayCases=document.querySelector(".todayCases");
const todayDeaths=document.querySelector(".todayDeaths");
const results = document.querySelector(".result-container");
results.style.display = "none";
loading.style.display = "none";
errors.textContent = "";
// grab the form
const form = document.querySelector(".form-data");
// grab the country name
const country = document.querySelector(".country-name");
// declare a method to search by country name
const searchForCountry = async countryName => {
  loading.style.display = "block";
  errors.textContent = "";
  try {
    const response = await axios.get(`${api}/${countryName}`);
    if(response.data ==="Country not found"){ throw error;  }
    loading.style.display = "none";
    todayCases.textContent = response.data.todayCases;
    todayDeaths.textContent = response.data.todayDeaths;
    cases.textContent = response.data.cases;
    recovered.textContent = response.data.recovered;
    deaths.textContent = response.data.deaths;
    tests.textContent =  response.data.totalTests;
    results.style.display = "block";
  } catch (error) {
    loading.style.display = "none";
    results.style.display = "none";
    errors.textContent = "We have no data for the country you have requested.";
  }
};
// declare a function to handle form submission
const handleSubmit = async e => {
  e.preventDefault();
  searchForCountry(country.value);
  console.log(country.value);
};
form.addEventListener("submit", e => handleSubmit(e));

上面，我们创建了一个名为searchForCountry的异步函数，在该函数上，我们可以使用async-await的语法。async await允许我们当正在等待服务端响应的时候，停止执行之后其他相关的代码。在代码片段前使用await关键字，当在执行该代码片段时，它之后的代码将停止执行。

在这个例子中，我们await一个GET请求的响应，然后将响应值赋值给response变量。

Axios是一个很受欢迎的JavaScript库，它可以很好处理HTTP请求，并且可以在浏览器平台和Node.js平台使用。它支持所有的现代浏览器，甚至支持IE8。它是基于promise的，所有很方便我们写async/await代码。

下面是些我们获取数据的API：

coronavirus-19-api.herokuapp.com/countries - 获取所有国家的详情
coronavirus-19-api.herokuapp.com/countries/i… - 获取印度这个国家的covid19案例信息

步骤4：创建CSS文件

根据个人的喜欢，编写对HTML进行装饰

步骤5：创建MANIFEST.JSON文件

创建一个名为manifest.json的文件，然后将下面的代码添加到文件中。这个文件包含了谷歌浏览器如何处理扩展程序的信息。

{
    "manifest_version": 2,
    "name": "Covid19",
    "version": "1.0.0",
    "description": "Provides the cases details regarding Covid19 with respective to any Country",
    "browser_action": {
      "default_popup": "index.html"
    },
    "icons":{
      "16": "./icons/16covid-19.png",
      "64": "./icons/64covid-19.png",
     "128": "./icons/128covid-19.png"
    },
    "content_security_policy": "script-src 'self' https://unpkg.com ; object-src 'self'"
}