 passed to this function.</li><li>Let <var>items</var> be the List of arguments passed to this function.</li><li>Let <var>weakset</var> be the <emu-val>this</emu-val> value.<ol><li>If Type(<var>weakset</var>) is not Object, throw a <emu-val>TypeError</emu-val> exception.</li></ol></li><li>Let <var>k</var> be 0.</li><li>Let <var>adder</var> be ?&nbsp;Get(<var>weakset</var>, "add")</li><li>If IsCallable(<var>adder</var>) is <emu-val>false</emu-val>, throw a <emu-val>TypeError</emu-val> exception.</li><li>Repe