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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 17-5 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 17-5 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>/** * InputFilter.js: unobtrusive filtering of keystrokes for <input> tags. * * This module finds all <input type="text"> elements in the document that * have a nonstandard attribute named "allowed". It registers an onkeypress * event handler for any such element to restrict the user's input so that * only characters that appear in the value of the allowed attribute may be * entered. If the <input> element also has an attribute named "messageid", * the value of that attribute is taken to be the id of another document * element. If the user types a character that is not allowed, the messageid * element is made visible. If the user types a character that is allowed, * the messageid element is hidden. This message id element is intended to * offer an explanation to the user of why her keystroke was rejected. It * should typically be styled with CSS so that it is initially invisible. * * Here is some example HTML that uses this module. * Zipcode: * <input id="zip" type="text" allowed="0123456789" messageid="zipwarn"> * <span id="zipwarn" style="color:red;visibility:hidden">Digits only</span> * * In browsers such as IE do not support addEventListener(), the * keypress handler registered by this module overwrites any keypress handler * defined in HTML. * * This module is purely unobtrusive: it does not define any symbols in * the global namespace. */(function() { // The entire module is within an anonymous function // When the document finishes loading, call the init() function below if (window.addEventListener) window.addEventListener("load", init, false); else if (window.attachEvent) window.attachEvent("onload", init); // Find all the <input> tags we need to register an event handler on function init() { var inputtags = document.getElementsByTagName("input"); for(var i = 0 ; i < inputtags.length; i++) { // Loop through all tags var tag = inputtags[i]; if (tag.type != "text") continue; // We only want text fields var allowed = tag.getAttribute("allowed"); if (!allowed) continue; // And only if they have an allowed attr // Register our event handler function on this input tag if (tag.addEventListener) tag.addEventListener("keypress", filter, false); else { // We don't use attachEvent because it does not invoke the // handler function with the correct value of the this keyword. tag.onkeypress = filter; } } } // This is the keypress handler that filters the user's input function filter(event) { // Get the event object and character code in a portable way var e = event || window.event; // Key event object var code = e.charCode || e.keyCode; // What key was pressed // If this keystroke is a function key of any kind, do not filter it if (e.charCode == 0) return true; // Function key (Firefox only) if (e.ctrlKey || e.altKey) return true; // Ctrl or Alt held down if (code < 32) return true; // ASCII control character // Now look up information we need from this input element var allowed = this.getAttribute("allowed"); // Legal chars var messageElement = null; // Message to hide/show var messageid = this.getAttribute("messageid"); // Message id, if any if (messageid) // If there is a message id, get the element messageElement = document.getElementById(messageid); // Convert the character code to a character var c = String.fromCharCode(code); // See if the character is in the set of allowed characters if (allowed.indexOf(c) != -1) { // If c is a legal character, hide the message, if any if (messageElement) messageElement.style.visibility = "hidden"; return true; // And accept the character } else { // If c is not in the set of allowed characters, display message if (messageElement) messageElement.style.visibility = "visible"; // And reject this keypress event if (e.preventDefault) e.preventDefault(); if (e.returnValue) e.returnValue = false; return false; } }})(); // Finish anonymous function and invoke it.</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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