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<!DOCTYPE html>
<html>
<body>
​
<h1>JavaScript 函数闭包</h1>
​
<p>使用局部变量计数。</p>
​
<p id="demo">0</p>
​
<script>
document.getElementById("demo").innerHTML = add();
function add() {
  var counter = 0;
  function plus() {counter += 1;}
  plus();  
  return counter; 
}
</script>
​
</body>
</html>
​