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<!DOCTYPE html>
<html>
<body>
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<h2>JavaScript Closures</h2>
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<p>Counting with a local variable.</p>
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<button type="button" onclick="myFunction()">Count!</button>
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<p id="demo">0</p>
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<script>
const add = (function () {
  let counter = 0;
  return function () {counter += 1; return counter;}
})();
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function myFunction(){
  document.getElementById("demo").innerHTML = add();
}
</script>
​
</body>
</html>
​