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author | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
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committer | Peter Bengtsson <mail@peterbe.com> | 2020-12-08 14:40:17 -0500 |
commit | 33058f2b292b3a581333bdfb21b8f671898c5060 (patch) | |
tree | 51c3e392513ec574331b2d3f85c394445ea803c6 /files/zh-cn/web/api/event/preventdefault | |
parent | 8b66d724f7caf0157093fb09cfec8fbd0c6ad50a (diff) | |
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diff --git a/files/zh-cn/web/api/event/preventdefault/index.html b/files/zh-cn/web/api/event/preventdefault/index.html new file mode 100644 index 0000000000..643b1be269 --- /dev/null +++ b/files/zh-cn/web/api/event/preventdefault/index.html @@ -0,0 +1,170 @@ +--- +title: event.preventDefault +slug: Web/API/Event/preventDefault +tags: + - API + - DOM + - Event + - preventDefault +translation_of: Web/API/Event/preventDefault +--- +<p>{{APIRef("DOM")}}</p> + +<p>{{domxref("Event")}} 接口的 <code><strong>preventDefault()</strong></code>方法,告诉{{Glossary("user agent")}}:如果此事件没有被显式处理,它默认的动作也不应该照常执行。此事件还是继续传播,除非碰到事件侦听器调用{{domxref("Event.stopPropagation", "stopPropagation()")}} 或{{domxref("Event.stopImmediatePropagation", "stopImmediatePropagation()")}},才停止传播。</p> + +<h3 id="Syntax" name="Syntax">语法</h3> + +<pre class="eval"><em>event</em>.preventDefault(); + +</pre> + +<h3 id="参数">参数</h3> + +<p>无</p> + +<h3 id="返回值">返回值</h3> + +<p><code>undefined</code></p> + +<h2 id="Example" name="Example">示例</h2> + +<h3 id="Blocking_default_click_handling" name="Blocking_default_click_handling">阻止默认的点击事件执行</h3> + +<p>选中复选框是点击复选框的默认行为。下面这个例子说明了怎样阻止默认行为的发生:</p> + +<h4 id="JavaScript">JavaScript</h4> + +<pre class="brush: js">document.querySelector("#id-checkbox").addEventListener("click", function(event) { + document.getElementById("output-box").innerHTML += "Sorry! <code>preventDefault()</code> won't let you check this!<br>"; + event.preventDefault(); +}, false);</pre> + +<h4 id="HTML">HTML</h4> + +<pre class="brush: html"><p>Please click on the checkbox control.</p> + +<form> + <label for="id-checkbox">Checkbox:</label> + <input type="checkbox" id="id-checkbox"/> +</form> + +<div id="output-box"></div></pre> + +<h4 id="结果">结果</h4> + +<p>你可以看到如下的行为:</p> + +<p>{{EmbedLiveSample("Blocking_default_click_handling")}}</p> + +<h3 id="Stopping_keystrokes_from_reaching_an_edit_field" name="Stopping_keystrokes_from_reaching_an_edit_field">在编辑域中阻止按键</h3> + +<p>下面的这个例子说明了如何使用<code>preventDefault()</code>在文本编辑域中阻止有效的文本输入。如今,你通常可以使用<a href="/zh-CN/docs/Learn/HTML/Forms/Data_form_validation">原生的HTML表单验证</a>来代替。</p> + +<h4 id="HTML_2">HTML</h4> + +<p>表单:</p> + +<pre class="brush: html"><div class="container"> + <p>Please enter your name using lowercase letters only.</p> + + <form> + <input type="text" id="my-textbox"> + </form> +</div></pre> + +<h4 id="CSS">CSS</h4> + +<p>当用户按下一个有效按键的时候,我们就给这个warning box 加上一些样式:</p> + +<pre class="brush: css">.warning { + border: 2px solid #f39389; + border-radius: 2px; + padding: 10px; + position: absolute; + background-color: #fbd8d4; + color: #3b3c40; +}</pre> + +<h4 id="JavaScript_2">JavaScript</h4> + +<p>这里是相关的JavaScript代码。首先,监听{{event("keypress")}}事件:</p> + +<pre class="brush: js"><code>var myTextbox = document.getElementById('my-textbox'); +myTextbox.addEventListener('keypress', checkName, false);</code></pre> + +<p> <code>checkName()</code>方法可以监听按键并且决定是否允许按键的默认行为发生。</p> + +<pre class="brush: js">function checkName(evt) { + var charCode = evt.charCode; + if (charCode != 0) { + if (charCode < 97 || charCode > 122) { + evt.preventDefault(); + displayWarning( + "Please use lowercase letters only." + + "\n" + "charCode: " + charCode + "\n" + ); + } + } +}</pre> + +<p><code>displayWarning()</code>方法显示了一个问题的通知。这不是一种优雅的方法,但是确实可以达到我们的目的。</p> + +<pre class="brush: js">var warningTimeout; +var warningBox = document.createElement("div"); +warningBox.className = "warning"; + +function displayWarning(msg) { + warningBox.innerHTML = msg; + + if (document.body.contains(warningBox)) { + window.clearTimeout(warningTimeout); + } else { + // insert warningBox after myTextbox + myTextbox.parentNode.insertBefore(warningBox, myTextbox.nextSibling); + } + + warningTimeout = window.setTimeout(function() { + warningBox.parentNode.removeChild(warningBox); + warningTimeout = -1; + }, 2000); +}</pre> + +<h4 id="结果_2">结果</h4> + +<p>这里就是代码的执行结果:</p> + +<p>{{ EmbedLiveSample('Stopping_keystrokes_from_reaching_an_edit_field', 600, 200) }}</p> + +<h2 id="备注"><font><font>备注</font></font></h2> + +<p>在事件流的任何阶段调用<code>preventDefault()</code>都会取消事件,这意味着任何通常被该实现触发并作为结果的默认行为都不会发生。</p> + +<p>你可以使用 {{domxref("Event.cancelable")}} 来检查该事件是否支持取消。为一个不支持cancelable的事件调用<code>preventDefault()</code>将没有效果。</p> + +<h2 id="Specifications" name="Specifications">规范</h2> + +<table class="standard-table"> + <thead> + <tr> + <th scope="col">规范</th> + <th scope="col">状态</th> + <th scope="col">注释</th> + </tr> + </thead> + <tbody> + <tr> + <td>{{SpecName('DOM WHATWG', '#dom-event-preventdefault', 'Event.preventDefault()')}}</td> + <td>{{ Spec2('DOM WHATWG') }}</td> + <td></td> + </tr> + <tr> + <td>{{SpecName('DOM2 Events', '#Events-Event-preventDefault', 'Event.preventDefault()')}}</td> + <td>{{ Spec2('DOM2 Events') }}</td> + <td>初版</td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容">浏览器兼容</h2> + +<p>{{Compat("api.Event.preventDefault")}}</p> |