---
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>