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      <base href="https://bugs.webkit.org/" />
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Object.preventExtensions makes code much slower"
   href="https://bugs.webkit.org/show_bug.cgi?id=143247">143247</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Object.preventExtensions makes code much slower
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>WebKit
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>528+ (Nightly build)
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Unspecified
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>Normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P2
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>JavaScriptCore
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>webkit-unassigned@lists.webkit.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>esprehn@chromium.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>If you have

class Foo {
  constructor() {
    this.property = 1;
    Object.preventExtensions(this);
  }
}

calling new Foo() seems to be 2-3x slower than doing so without the call to preventExtensions. This is not the case in v8 or Firefox. This pattern is really nice since it catches bad assignments and typos in code.</pre>
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