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--- docs:programming:javascript:typeof [2007/07/15 21:34] – created billh
+++ docs:programming:javascript:typeof [2008/08/03 00:25] (current) – external edit 127.0.0.1
@@ Line 8: / Line 8: @@
 alert(typeof NumericalValue) // displays "number"
 alert(typeof StringValue) // displays "string"
+</code>
+===== checking for existence =====
+<code javascript>
+if( typeof addEvent != 'undefined' ){
+// addEvent method exists, and is okay to use here
+}
+</code>
+===== typeof with document.getElementById =====
+Do NOT use the following:
+<code javascript>
+if( typeof document.getElementById('someElementId') != 'undefined' ){
+// do something with element
+}
+</code>
+...because getElementById() is a method which incorporates its own typeof checking.  If an element doesn't exist, it will still return 'Object', because null is what is returned and it is an Object in itself.  Instead, simply do this:
+<code javascript>
+if( document.getElementById('someElementId') != null ){
+// do something with element
+}
+// or
+var el = document.getElementById('someElementId');
+if( el ){
+// do something with element
+}
 </code>