​x
 
<!DOCTYPE html>
<html>
<body>
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<h1>Document 对象</h1>
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<h2>hasFocus() 方法</h2>
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<p>单击此文档内部可获得焦点。<br>
单击此文档外部可失去焦点。</p>
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<p id="demo"></p>
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<script>
setInterval("myFunction()", 1);
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function myFunction() {
  let text;
  if (document.hasFocus()) {
    text = "本文档获得焦点。";
  } else {
    text = "本文档未获得焦点。";
  }
document.getElementById("demo").innerHTML = text;
}
</script>
​
</body>
</html>
​