JSObjectProxy>>at:ifAbsent: take care of property which is set to 'undefined' (as suggested by Herby)

js/Kernel-Objects.deploy.js

@@ -1474,9 +1474,9 @@ selector: "at:ifAbsent:",
 fn: function (aSymbol,aBlock){
 var self=this;
 return smalltalk.withContext(function($ctx1) { 
-    	var value = self['@jsObject'][aSymbol._asString()];
-        if (undefined === value) return aBlock();
-        return value;
+    	var obj = self['@jsObject'],
+        	symbol = aSymbol._asString();
+		return symbol in obj ? obj[symbol] : aBlock();
 	;
 return self}, function($ctx1) {$ctx1.fill(self,"at:ifAbsent:",{aSymbol:aSymbol,aBlock:aBlock}, smalltalk.JSObjectProxy)})}
 }),

js/Kernel-Objects.js

@@ -2064,13 +2064,13 @@ category: 'accessing',
 fn: function (aSymbol,aBlock){
 var self=this;
 return smalltalk.withContext(function($ctx1) { 
-    	var value = self['@jsObject'][aSymbol._asString()];
-        if (undefined === value) return aBlock();
-        return value;
+    	var obj = self['@jsObject'],
+        	symbol = aSymbol._asString();
+		return symbol in obj ? obj[symbol] : aBlock();
 	;
 return self}, function($ctx1) {$ctx1.fill(self,"at:ifAbsent:",{aSymbol:aSymbol,aBlock:aBlock}, smalltalk.JSObjectProxy)})},
 args: ["aSymbol", "aBlock"],
-source: "at: aSymbol ifAbsent: aBlock\x0a\x09\x22return the aSymbol property or evaluate aBlock if the property is undefined\x22\x0a\x09<\x0a    \x09var value = self['@jsObject'][aSymbol._asString()];\x0a        if (undefined === value) return aBlock();\x0a        return value;\x0a\x09>",
+source: "at: aSymbol ifAbsent: aBlock\x0a\x09\x22return the aSymbol property or evaluate aBlock if the property is not defined on the object\x22\x0a\x09<\x0a    \x09var obj = self['@jsObject'],\x0a        \x09symbol = aSymbol._asString();\x0a\x09\x09return symbol in obj ? obj[symbol] : aBlock();\x0a\x09>",
 messageSends: [],
 referencedClasses: []
 }),

st/Kernel-Objects.st

@@ -673,11 +673,11 @@ at: aSymbol
 !
 
 at: aSymbol ifAbsent: aBlock
-	"return the aSymbol property or evaluate aBlock if the property is undefined"
+	"return the aSymbol property or evaluate aBlock if the property is not defined on the object"
 	<
-    	var value = self['@jsObject'][aSymbol._asString()];
-        if (undefined === value) return aBlock();
-        return value;
+    	var obj = self['@jsObject'],
+        	symbol = aSymbol._asString();
+		return symbol in obj ? obj[symbol] : aBlock();
 	>
 !