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POHow come this line of code returns me an "undefined" then followed by a value
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  1. POHow come this line of code returns me an "undefined" then followed by a value
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    copied!<p>How come method equal always returns with an "undefined" followed by a number? and when I try to parse it. it returns me a NaN.</p> <pre><code>&lt;!DOCTYPE&gt; &lt;html&gt; &lt;head&gt; &lt;script&gt; var fnum; var secondNum; var operation; function msg(val) { document.getElementById("fnumtext").value += val; fnum += val; } function showOperation(oper) { document.getElementById("fnumtext").value = ""; document.getElementById("operation").value = oper; operation = oper; } function equal() { secondNum = document.getElementById("fnumtext").value; alert(fnum); } &lt;/script&gt; &lt;/head&gt; &lt;body&gt; &lt;input id = "fnumtext"type="text" name="firstnum" /&gt;&lt;br /&gt; &lt;input id = "operation" type="text" name="secondnum" /&gt;&lt;br /&gt; &lt;input type="button" value="1" onclick="msg('1')" /&gt; &lt;input type="button" value="2" onclick="msg('2')" /&gt; &lt;input type="button" value="3" onclick="msg('3')" /&gt;&lt;/br&gt; &lt;input type="button" value="4" onclick="msg('4')" /&gt; &lt;input type="button" value="5" onclick="msg('5')" /&gt; &lt;input type="button" value="6" onclick="msg('6')" /&gt;&lt;br/&gt; &lt;input type="button" value="7" onclick="msg('7')" /&gt; &lt;input type="button" value="8" onclick="msg('8')" /&gt; &lt;input type="button" value="9" onclick="msg('9')" /&gt;&lt;/br&gt; &lt;input type="button" value="0" onclick="msg('0')" /&gt;&lt;/br&gt; &lt;input type="button" value="+" onclick="showOperation('+')" /&gt; &lt;input type="button" value="*" onclick="showOperation('*')" /&gt; &lt;input type="button" value="/" onclick="showOperation('/')" /&gt; &lt;input type="button" value="-" onclick="showOperation('-')" /&gt; &lt;input type="button" value="=" onclick="equal()" /&gt; &lt;/body&gt; &lt;/html&gt; </code></pre>
 

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