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<meta·charset="utf-8">·
<title>W3Cschool(w3cschool.cn)</title>·
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<button type="button" autofocus onclick="alert('Hello world!')">点我</button>
<p><strong>注意：</strong> Internet Explorer 9 以及更早 IE 版本不支持 autofocus 属性。</p>
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