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Sharing of usage examples of isNAN()

零下一度Original: 2017-07-02 09:21:221448browse

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

<script>
    function myfunction() {
       var t=document.getElementById("demo2").value;

        if(t==""||isNaN(t)){
            alert("不是数字");
        }
        else return;
    }

</script>


</head>








<body>
<h1>我的第一个 JavaScript 程序</h1>
<p id="demo">请输入数字。如果输入值不是数字，浏览器会弹出提示框。</p>
<input type="text" id="demo2">
<button type="button" onclick="myfunction()">click</button>
</body>
</html>

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