css会造成阻塞吗（文档解析DOMContentLoaded,onload）结论不阻塞dom树解析阻塞dom树渲染

结论

不阻塞dom树解析
阻塞dom树渲染
阻塞js执行

DOMContentLoaded,html文档加载解析完之后执行

        document.addEventListener('DOMContentLoaded',function() {
            console.log('DOMContentLoaded')
        })

onload,页面所有资源加载完之后执行

        window.onload = function() {
            console.log('onload')
        }

实践

限制network上传下行速度 demo.html

<!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">
    <title>Document</title>
    <script>
        window.onload = function() {
            console.log('onload')
        }
        document.addEventListener('DOMContentLoaded',function() {
            console.log('DOMContentLoaded')
        })

    </script>
    <link href="https://cdn.bootcss.com/bootstrap/4.0.0-alpha.6/css/bootstrap.css" rel="stylesheet">
    <script defer>
        console.log('hh')
    </script>
</head>
<body>
</body>
</html>