实例代码“Ctrl+/”提示“F11/ESC”全屏 返回 格式化 恢复 运行
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<!DOCTYPE html>
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<html>
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<head>
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    <title>Execution Context Example 4</title>
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    <script type="text/javascript">
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        function add(num1, num2) {
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            var sum = num1 + num2;
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            return sum;
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        }
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        var result = add(10, 20);  //30
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        alert(sum);                //causes an error since sum is not a valid variable
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​
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    </script>
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​
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</head>
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<body>
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</body>
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</html>