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<!DOCTYPE html>
<html>
<body>
​
<button onClick="myTimer = setInterval(myCounter, 1000)">启动计数器</button>
​
<p id="demo">点击上面的按钮，我会永远计数。</p>
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<button onClick="clearInterval(myTimer)">停止计数器</button>
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<script>
var c = 0;
function myCounter() {
  document.getElementById("demo").innerHTML = ++c;
}
</script> 
​
</body>
</html>
​