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<html><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Keywords" name="Keywords"content="JavaScript, examples, JavaScript: The Definitive Guide"><title>Example 18-3 from JavaScript: The Definitive Guide, Fifth Edition</title><style>body { font-family: arial, sans-serif}.lefttitle { font: bold x-small arial, sans-serif; margin: 5px; letter-spacing: .15em; text-transform:uppercase;}.leftcaption { font: italic x-small sans-serif; margin-bottom: 20px;}#banner { font-family:sans-serif; color:#333; font-size:x-large; font-weight:normal; padding:15px; padding-top: 3px; border-bottom:4px double #666;}#banner h1 { font-size: x-large; margin: 0px; padding: 0px;}#banner .description { font-size:large; margin-left: 2px;}pre { border: solid black 1px; background-color: #ddd; padding: 10px; margin: 0px;} </style></script></head><body><div id="banner"><h1>davidflanagan.com/javascript5</h1><span class="description">Example 18-3 from<i>JavaScript: The Definitive Guide, Fifth Edition</i></span></div><div style="float: left; 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text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><pre>/** * Validate.js: unobtrusive HTML form validation. * * On document load, this module scans the document for HTML forms and * textfield form elements. If it finds elements that have a "required" or * "pattern" attribute, it adds appropriate event handlers for client-side * form validation. * * If a form element has a "pattern" attribute, the value of that attribute * is used as a JavaScript regular expression, and the element is given an * onchange event handler that tests the user's input against the pattern. * If the input does not match the pattern, the background color of the * input element is changed to bring the error to the user's attention. * By default, the textfield value must contain some substring that matches * the pattern. If you want to require the complete value to match precisely, * use the ^ and $ anchors at the beginning and end of the pattern. * * A form element with a "required" attribute must have a value provided. * The presence of "required" is shorthand for pattern="\S". That is, it * simply requires that the value contain a single non-whitespace character * * If a form element passes validation, its "class" attribute is set to * "valid". And if it fails validation, its class is set to "invalid". * In order for this module to be useful, you must use it in conjunction with * a CSS stylesheet that defines styles for "invalid" class. For example: * * <!-- attention grabbing orange background for invalid form elements --> * <style>input.invalid { background: #fa0; }</style> * * When a form is submitted the textfield elements subject to validation are * revalidated. If any fail, the submission is blocked and a dialog box * is displayed to the user letting him know that the form is incomplete * or incorrect. * * You may not use this module to validate any form fields or forms on which * you define your own onchange or onsubmit event handlers, or any fields * for which you define a class attribute. * * This module places all its code within an anonymous function and does * not define any symbols in the global namespace. */(function() { // Do everything in this one anonymous function // When the document finishes loading, call init() if (window.addEventListener) window.addEventListener("load", init, false); else if (window.attachEvent) window.attachEvent("onload", init); // Define event handlers for any forms and form elements that need them. function init() { // Loop through all forms in the document for(var i = 0; i < document.forms.length; i++) { var f = document.forms[i]; // the form we're working on now // Assume, for now, that this form does not need any validation var needsValidation = false; // Now loop through the elements in our form for(j = 0; j < f.elements.length; j++) { var e = f.elements[j]; // the element we're working on // We're only interested in <input type="text"> textfields if (e.type != "text") continue; // See if it has attributes that require validation var pattern = e.getAttribute("pattern"); // We could use e.hasAttribute() but IE doesn't support it var required = e.getAttribute("required") != null; // Required is just a shortcut for a simple pattern if (required && !pattern) { pattern = "\\S"; e.setAttribute("pattern", pattern); } // If this element requires validation, if (pattern) { // validate the element each time it changes e.onchange = validateOnChange; // Remember to add an onsubmit handler to this form needsValidation = true; } } // If at least one of the form elements needed validation, // we also need an onsubmit event handler for the form if (needsValidation) f.onsubmit = validateOnSubmit; } } // This function is the onchange event handler for textfields that // require validation. Remember that we converted the required attribute // to a pattern attribute in init(). function validateOnChange() { var textfield = this; // the textfield var pattern = textfield.getAttribute("pattern"); // the pattern var value = this.value; // the user's input // If the value does not match the pattern set the class to "invalid". if (value.search(pattern) == -1) textfield.className = "invalid"; else textfield.className = "valid"; } // This function is the onsubmit event handler for any form that // requires validation. function validateOnSubmit() { // When the form is submitted, we revalidate all the fields in the // form and then check their classNames to see if they are invalid. // If any of those fields are invalid, display an alert and prevent // form submission. var invalid = false; // Start by assuming everything is valid // Loop through all form elements for(var i = 0; i < this.elements.length; i++) { var e = this.elements[i]; // If the element is a text field and has our onchange handler if (e.type == "text" && e.onchange == validateOnChange) { e.onchange(); // Invoke the handler to re-validate // If validation fails for the element, it fails for the form if (e.className == "invalid") invalid = true; } } // If the form is invalid, alert user and block submission if (invalid) { alert("The form is incompletely or incorrectly filled out.\n" + "Please correct the highlighted fields and try again."); return false; } }})();</pre><div class="lefttitle" style="padding:0px; text-align: right"><a href="index.html" tppabs="http://www.davidflanagan.com/javascript5/index.html">Table of Examples</a></div><p><script type="text/javascript">amazon_ad_tag="davidflanagancom"; amazon_ad_width="300"; amazon_ad_height="250"; amazon_ad_logo="hide";</script><script type="text/javascript" src="../../www.assoc-amazon.com/s/ads.js" tppabs="http://www.assoc-amazon.com/s/ads.js"></script></div></body></html>⌨️ 快捷键说明
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