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<!DOCTYPE html>
<html>
<body>
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<p>单击按钮以评估/执行 JavaScript 代码/表达式。</p>
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<button onclick="myFunction()">试一试</button>
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<p id="demo"></p>
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<script>
function myFunction() {
  var x = 10;
  var y = 20;
  var a = eval("x * y") + "<br>";
  var b = eval("2 + 2") + "<br>";
  var c = eval("x + 17") + "<br>";
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  var res = a + b + c;
  document.getElementById("demo").innerHTML = res;
}
</script>
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</body>
</html>
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