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+---
+title: IDBKeyRange.lowerBound()
+slug: Web/API/IDBKeyRange/lowerBound
+translation_of: Web/API/IDBKeyRange/lowerBound
+---
+<p>{{ APIRef("IndexedDB") }}</p>
+
+<div>
+<p>{{domxref("IDBKeyRange")}} 接口的<strong><code>lowerBound()</code></strong>方法创建一个只有下限的新的键范围。默认情况下，它包含较低的端点值。</p>
+</div>
+
+<p>{{AvailableInWorkers}}</p>
+
+<h2 id="Syntax">Syntax</h2>
+
+<pre class="syntaxbox" style="font-size: 14px;">var <em>myIDBKeyRange</em> = <em>IDBKeyRange</em>.lowerBound(<em>lower</em>);
+var <em>myIDBKeyRange</em> = <em>IDBKeyRange</em>.lowerBound(<em>lower</em>, <em>open</em>);
+</pre>
+
+<h3 id="Parameters">Parameters</h3>
+
+<dl>
+ <dt>lower </dt>
+ <dd>指定新键范围的下限。</dd>
+ <dt>open<em> </em>{{optional_inline}}</dt>
+ <dd>指示下限是否排除端点值。默认值为false。</dd>
+</dl>
+
+<h3 id="Return_value">Return value</h3>
+
+<p>{{domxref("IDBKeyRange")}}: 新创建的键范围.</p>
+
+<h3 id="Exceptions">Exceptions</h3>
+
+<p>此方法可能引发以下类型的 {{domxref("DOMException")}} :</p>
+
+<table class="standard-table">
+ <thead>
+  <tr>
+   <th scope="col">Exception</th>
+   <th scope="col">Description</th>
+  </tr>
+ </thead>
+ <tbody>
+  <tr>
+   <td><font face="Courier New, Andale Mono, monospace"><span style="line-height: normal;">DataError</span></font></td>
+   <td>
+    <p>The value parameter passed was not a valid key.</p>
+
+    <div></div>
+   </td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Example">Example</h2>
+
+<p>下面的示例演示如何使用下限键范围。在这里，我们声明<code>keyRangeValue = IDBKeyRange.lowerBound("F", false);</code>— 一个包含值“F”及其后所有内容的范围。我们打开一个事务（使用 {{domxref("IDBTransaction")}}）和一个对象存储，并使用 {{domxref("IDBObjectStore.openCursor")}}打开一个游标，声明<code>keyRangeValue</code> 为其可选的键范围值。这意味着光标将只检索键值为“F”及其后面的所有记录。如果使用<code>IDBKeyRange.lowerBound("F", true);</code>，则该范围将不包括端点“F”，仅包括其后面的值。</p>
+
+<div class="note">
+<p><strong>Note</strong>: 要获得一个更完整的示例，使您能够使用键范围进行实验，请查看我们的 <a href="https://github.com/mdn/indexeddb-examples/tree/master/idbkeyrange">IDBKeyRange-example</a>（<a href="https://mdn.github.io/indexeddb-examples/idbkeyrange/">实时查看该示例</a>）。</p>
+</div>
+
+<pre class="brush: js" style="font-size: 14px;">function displayData() {
+  var keyRangeValue = IDBKeyRange.lowerBound("F");
+
+  var transaction = db.transaction(['fThings'], 'readonly');
+  var objectStore = transaction.objectStore('fThings');
+
+  objectStore.openCursor(keyRangeValue).onsuccess = function(event) {
+    var cursor = event.target.result;
+      if(cursor) {
+        var listItem = document.createElement('li');
+        listItem.innerHTML = '&lt;strong&gt;' + cursor.value.fThing + '&lt;/strong&gt;, ' + cursor.value.fRating;
+        list.appendChild(listItem);
+
+        cursor.continue();
+      } else {
+        console.log('Entries all displayed.');
+      }
+    };
+  };</pre>
+
+<div></div>
+
+<h2 id="Specification">Specification</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">Specification</th>
+   <th scope="col">Status</th>
+   <th scope="col">Comment</th>
+  </tr>
+  <tr>
+   <td>{{SpecName('IndexedDB', '#widl-IDBKeyRange-lowerBound-IDBKeyRange-any-lower-boolean-open', 'lowerBound()')}}</td>
+   <td>{{Spec2('IndexedDB')}}</td>
+   <td></td>
+  </tr>
+  <tr>
+   <td>{{SpecName("IndexedDB 2", "#dom-idbkeyrange-lowerbound-lower-open-lower", "lowerBound()")}}</td>
+   <td>{{Spec2("IndexedDB 2")}}</td>
+   <td></td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility" name="Browser_compatibility">Browser compatibility</h2>
+
+<div>
+
+
+<p>{{Compat("api.IDBKeyRange.lowerBound")}}</p>
+</div>
+
+<h2 id="See_also">See also</h2>
+
+<ul>
+ <li><a href="/en-US/docs/Web/API/IndexedDB_API/Using_IndexedDB">Using IndexedDB</a></li>
+ <li>Starting transactions: {{domxref("IDBDatabase")}}</li>
+ <li>Using transactions: {{domxref("IDBTransaction")}}</li>
+ <li>Setting a range of keys: {{domxref("IDBKeyRange")}}</li>
+ <li>Retrieving and making changes to your data: {{domxref("IDBObjectStore")}}</li>
+ <li>Using cursors: {{domxref("IDBCursor")}}</li>
+ <li>Reference example: <a class="external" href="https://github.com/mdn/to-do-notifications/tree/gh-pages">To-do Notifications</a> (<a class="external" href="http://mdn.github.io/to-do-notifications/">view example live</a>.)</li>
+</ul>