rst</var> be <emu-val>true</emu-val> and <var>initialValue</var> is not present:<ol><li>Set <var>accumulator</var> to <var>e</var></li></ol></li><li>Else,<ol><li>Set <var>accumulator</var> to ?&nbsp;Call(<var>callbackfn</var>, undefined, « <var>accumulator</var>, <var>e</var>, <var>e</var>, <var>map</var>&nbsp;»)</li></ol></li><li>Set <var>first</var> to <emu-val>false</emu-val></li></ol></li></ol></li><li>If <var>first</var> is <emu-val>true</emu-val> and <var>initialValue</var> is not present, throw <em