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Judge whether the string is empty

2022-06-28 19:21:00 【liaowenxiong】

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title> Check if the specified value is an empty string </title>
    <script>
        function test_1() {
    
            // var name = document.getElementById("name").value;
            // alert(name);
            var name = null;
            // var flag = isEmptyStr(name);
            var flag = isEmptyStrV2(name);
            alert(flag);
        }
        function test_2() {
    
            var flag_1 = null == undefined; // true
            var flag_2 = null === undefined; // false
            alert(flag_1);
            alert(flag_2);
        }

        function test_3(s) {
    
            alert(s);
            var flag = isEmptyStr(s);
            alert(flag);

        }


        function isEmptyStr(s) {
    
            if (s == undefined || s == null || s.trim() === '') {
    
                return true
            }
            return false
        }

        function isEmptyStrV2(s) {
    
            if (typeof s == 'string' && s.trim().length == 0) {
    
                return true;
            } else if (s == null) {
    
                return true;
            }
            return false;
        }

        //  Because the program will null Equate to undefined, So you can add the above function to if The conditional statement in the statement is simplified to the conditional statement shown in the following function 
        function isEmptyStr(s) {
    
            if (s == undefined || s.trim() === '') {
    
                return true
            }
            return false
        }


    </script>
</head>
<body>
<label for="name">name:</label>
<input id="name" type="text" name="name"/>
<button type="button" onclick="var name = document.getElementById('name').value;test_3(name);">Click Me!</button>
<!--<button type="button" onclick="test_1();">Click Me!</button>-->
<!--<button type="button" onclick="test_2();">Click Me!</button>-->
</body>
</html>

Reference resources ：https://blog.csdn.net/K346K346/article/details/113182838

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本文为[liaowenxiong]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/179/202206281907425443.html

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Judge whether the string is empty

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