在vue-cli生成的项目中，index.html下是无法直接获取到环境变量的，但是可以使用webpack提供的特殊语法获取的服务中的变量 <% %>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width,initial-scale=1.0" />
<meta name="keywords" content="" />
<meta name="description" content="" />
<link rel="icon" href="<%= BASE_URL %>favicon.ico" />
<title><%= htmlWebpackPlugin.options.title %></title>
<% if (process.env.NODE_ENV === 'production' ) { %>
<script>
code.....
</script>
<% } else {%>
<script>
code.....
</script>
<% } %>
</head>
<body>
<noscript>
<strong>We're sorry but <%= htmlWebpackPlugin.options.title %> doesn't work properly without JavaScript enabled. Please enable it to continue.</strong>
</noscript>
<div id="app"></div>
<!-- built files will be auto injected -->
</body>
</html>
