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<!DOCTYPE html>
<html>
<body>
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<h1>JavaScript 变量</h1>
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<p>如果您再次声明某个 JavaScript 变量，那么它的值不会丢失。</p>
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<p id="demo"></p>
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<script>
var carName = "porsche";
var carName;
document.getElementById("demo").innerHTML = carName;
</script>
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</body>
</html>
​