Programming Tutorials

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Form validation using Javascript

By: David Flanagan in Javascript Tutorials on 2008年08月31日 [フレーム]

The <form> tag supports an onsubmit event handler, which is triggered when the user tries to submit a form. You can use this event handler to perform validation: checking that all required fields have been filled in, for example. If the onsubmit handler returns false, the form is not submitted. For example:

<form name="address" onsubmit="checkAddress()">
 <!-- form elements go here -->
</form>
<script>
 // A simple form validation function
 function checkAddress() {
 var f = document.address; // The form to check
 // Loop through all elements
 for (var i = 0; i < f.elements.length; i++) {
 // Ignore all but text input elements
 if (f.elements[i].type != "text") continue;
 // Get the user's entry
 var text = f.elements[i].value;
 // If it is not filled in, alert the user
 if (text == null || text.length == 0) {
 alert("Please fill in all form fields.");
 return false;
 }
 }
 }
</script>

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