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                # JavaScript 表單驗證 **JavaScript 可用來在數據被送往服務器前對 HTML 表單中的這些輸入數據進行驗證。** ## JavaScript 表單驗證 JavaScript 可用來在數據被送往服務器前對 HTML 表單中的這些輸入數據進行驗證。 被 JavaScript 驗證的這些典型的表單數據有: * 用戶是否已填寫表單中的必填項目? * 用戶輸入的郵件地址是否合法? * 用戶是否已輸入合法的日期? * 用戶是否在數據域 (numeric field) 中輸入了文本? ## 必填(或必選)項目 下面的函數用來檢查用戶是否已填寫表單中的必填(或必選)項目。假如必填或必選項為空,那么警告框會彈出,并且函數的返回值為 false,否則函數的返回值則為 true(意味著數據沒有問題): ``` function validate_required(field,alerttxt) { with (field) { if (value==null||value=="") {alert(alerttxt);return false} else {return true} } } ``` 下面是連同 HTML 表單的代碼: ``` <html> <head> <script type="text/javascript"> `function validate_required(field,alerttxt) { with (field) { if (value==null||value=="") {alert(alerttxt);return false} else {return true} } } function validate_form(thisform) { with (thisform) { if (validate_required(email,"Email must be filled out!")==false) {email.focus();return false} } }` </script> </head> <body> <form action="submitpage.htm" onsubmit="return validate_form(this)" method="post"> Email: <input type="text" name="email" size="30"> <input type="submit" value="Submit"> </form> </body> </html> ``` ## E-mail 驗證 下面的函數檢查輸入的數據是否符合電子郵件地址的基本語法。 意思就是說,輸入的數據必須包含 @ 符號和點號(.)。同時,@ 不可以是郵件地址的首字符,并且 @ 之后需有至少一個點號: ``` function validate_email(field,alerttxt) { with (field) { apos=value.indexOf("@") dotpos=value.lastIndexOf(".") if (apos<1||dotpos-apos<2) {alert(alerttxt);return false} else {return true} } } ``` 下面是連同 HTML 表單的完整代碼: ``` <html> <head> <script type="text/javascript"> `function validate_email(field,alerttxt) { with (field) { apos=value.indexOf("@") dotpos=value.lastIndexOf(".") if (apos<1||dotpos-apos<2) {alert(alerttxt);return false} else {return true} } } function validate_form(thisform) { with (thisform) { if (validate_email(email,"Not a valid e-mail address!")==false) {email.focus();return false} } }` </script> </head> <body> <form action="submitpage.htm"onsubmit="return validate_form(this);" method="post"> Email: <input type="text" name="email" size="30"> <input type="submit" value="Submit"> </form> </body> </html> ```
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