Javascript generic clone() method used in GWT application
I was trying to write a generic clone function which should be able to do true deep cloning. I have come across this link, How to Deep clone in javascript and took the function from there.
That code workds pretty well when I try using direct Javascript. I did minor modifications in the code and tried to put in the JSNI code in GWT.
clone function:
deepCopy = function(item)
{
if (!item) {
return item;
} // null, undefined values check
var types = [ Number, String, Boolean ], result;
// normalizing primitives if someone did new String('aaa'), or new Number('444');
types.forEach(function(type) {
if (item instanceof type) {
result = type(item);
}
});
if (typeof result == "undefined") {
alert(Object.prototype.toString.call(item));
alert(item);
alert(typeof item);
if (Object.prototype.toString.call(item) === "[object GWTJavaObject]") {
alert('1st');
result = [];
alert('2nd');
item.forEach(function(child, index, array) {//exception thrown here
alert('inside for each');
result[index] = deepCopy(child);
});
} else if (typeof item == "GWTJavaObject") {
alert('3rd');
if (item.nodeType && typeof item.cloneNode == "function") {
var result = item.cloneNode(true);
} else if (!item.prototype) {
result = {};
for ( var i in item) {
result[i] = deepCopy(item[i]);
}
} else {
if (false && item.constructor) {
result = new item.constructor();
} else {
result = item;
}
}
} else {
alert('4th');
result = item;
}
}
return result;
}
And the list am passing to this function is like this:
List<Integer> list = new ArrayList<Integer>();
list.add( new Integer( 100 ) );
list.add( new Integer( 200 ) );
list.add( new Integer( 300 ) );
List<Integer> newList = ( List<Integer> ) new Attempt().clone( list );
Integer temp = new Integer( 500 );
list.add( temp );
if ( newList.contains( temp ) )
Window.alert( "fail" );
else
Window.alert( "success" );
But when I execute this, I get null pointer exception in the clone function immediately after alert("2nd") line.
Kindly help.
PS: I am trying to get a generic clone method here that can be used to clone any object.
GWT prototyped objects don't have a forEach method; they do not inherit standard javascript object prototypes, as they are supposed to act like java objects, not javascript objects.
You could probably get away with Object.prototype.forEach.call(item, function(){})
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