Web AppBuilder Custom Widget - Cannot read property 'graphics' of undefined

XuanKuai

I'm developing a custom widget that can select and highlight ZIP Code area on pressing the Enter key after entering the ZIP Code. But the map seems always to be undefined. The code is shown below:

onEnterKeyUp<SPAN class="punctuation token">:</SPAN> <SPAN class="keyword token">function</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN> <SPAN class="comment token">// Draw selected ZIP Code area on pressing Enter</SPAN>
  <SPAN class="token function">on</SPAN><SPAN class="punctuation token">(</SPAN>dom<SPAN class="punctuation token">.</SPAN><SPAN class="token function">byId</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">"zip_box"</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">'keyup'</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="keyword token">function</SPAN><SPAN class="punctuation token">(</SPAN>event<SPAN class="punctuation token">)</SPAN> <SPAN class="punctuation token">{</SPAN>
    <SPAN class="keyword token">var</SPAN> input <SPAN class="operator token">=</SPAN> document<SPAN class="punctuation token">.</SPAN><SPAN class="token function">getElementById</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="string token">"zip_box"</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">.</SPAN>value<SPAN class="punctuation token">;</SPAN>

    <SPAN class="keyword token">if</SPAN> <SPAN class="punctuation token">(</SPAN>event<SPAN class="punctuation token">.</SPAN>keyCode <SPAN class="operator token">===</SPAN> <SPAN class="number token">13</SPAN><SPAN class="punctuation