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<!DOCTYPE html>
<html>
<body>
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<p>单击该按钮可循环遍历拥有四个元素的数组的索引，但当 i 等于“3”时退出循环。</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 cars = ["BMW", "Volvo", "Saab", "Ford"];
  var text = "";
  var i;
  for (i = 0;; i++) {
    if (i == 3) {
      break;
    }
    text += cars[i] + "<br>";
  }
​
  document.getElementById("demo").innerHTML = text;
}
</script>
​
</body>
</html>
​