     <emu-import href="./map/prototype-reduce.html"><p>When the <code>reduce</code> method is called, the following steps are taken:</p><emu-alg><ol><li>Let <var>map</var> be the <emu-val>this</emu-val> value.<ol><li>If Type(<var>map</var>) is not Object, throw a <emu-val>TypeError</emu-val> exception.</li><li>If <var>map</var> does not have a <emu-const><var class="field">[[MapData]]</var></emu-const> internal slot, throw a <emu-val>TypeError</emu-val> exception.</li></ol></li><li>If IsCallable(<var>callba