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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 - [JSC] Default parameter part should be retrieved by op_get_argument opcode instead of changing parity"
   href="https://bugs.webkit.org/show_bug.cgi?id=164582">164582</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>[JSC] Default parameter part should be retrieved by op_get_argument opcode instead of changing parity
          </td>
        </tr>

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

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

        <tr>
          <th>Version</th>
          <td>WebKit 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&#64;lists.webkit.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>utatane.tea&#64;gmail.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>If you have a function like,

function func(a, b, options = {}) {
...
}

`func.length` is 2. But the number of parameters of this function is counted as 3.
So if you call it with the form `func(a, b)`, the arity check always fails.
But in the above case, not passing options is common.

Instead, we should retrieve the argument by using `op_get_argument`. It does not increase the arity.</pre>
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      </p>
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