I confirmed this issue in the versions you've listed.  However, since it's currently
fixed in both v2.x and v2, I'm closing it for now and will reopen it if needed.

This issue reoccurs in version 3 javascript API:
<script src="http://maps.google.com/maps/api/js?sensor=false" type="text/javascript"></script>
 
I use the following utility methods:
	Object.prototype.isArray = function(){
		return this.constructor === Array.prototype.constructor;
	};
	Object.prototype.getNextSibling = function(){
		var endBrother = this.nextSibling;
		while(endBrother.nodeType !== 1){ endBrother = endBrother.nextSibling; }
		return endBrother;
	};
	Object.prototype.getFirstChild = function(){
		var firstChild = this.firstChild;
		while(firstChild.nodeType !== 1){ firstChild = firstChild.nextSibling; }
		return firstChild;
	};

any one of which (or any other custom method added to Object) inhibits Google Maps completely. 

Error is thrown on trying to execute:

	var canvas = document.getElementById('map_canvas');//OK - element exists
	var map = new google.maps.Map(canvas);//throws error

regardless of whether the methods are defined before or after the Google maps script tag (see above).

FF 3.6.12 (Win 2000):
Error: Invalid value: [object Object] (Invalid value for property <isArray>: function () {
    return this.constructor === Array.prototype.constructor;
})
Source File: http://maps.gstatic.com/intl/en_us/mapfiles/api-3/3/2/main.js
Line: 16

Opera 10.63 (Win 2000):
Uncaught exception: Error: Invalid value: [object Object] (Invalid value for property <isArray>: function(){
		return this.constructor === Array.prototype.constructor;
	})
Error thrown at line 1, column 39 in aa(a):
    throw a;
called from line 16, column 194 in <anonymous function>():
    aa(ia("Invalid value: "+(arguments[0]+(" ("+(c[kc](" | ")+")")))));
called from line 25, column 1796 in <anonymous function>(c):
    if(!b(c))
called from line 32, column 1210 in eg(a, b):
    c.setPov(new bg(0,0,1));
called from line 32, column 2787 in lg(a, b):
    c.l=new eg(a,{visible:l,enableCloseButton:i,Aa:this.Aa});
called from line 23, column 1 in <anonymous function: onload>() in file://localhost/E:/My%20Documents/Others/Andrea/hurtigruten_desktop_reference/hurtigruten.html:
    var map = new google.maps.Map(canvas);

IE6 (Win 2000): 
Invalid value: [object Object] (Invalid value for property <isArray>: function () {
    return this.constructor === Array.prototype.constructor;
})

This is pretty major as the workaround(s) would be extensive and involved.

I'm going to repurpose this issue for v3, but in the future could you please file a separate issue because v2 and v3 are completely different.

I certainly do not recommend modifying any built-in prototypes, however I'll take a further look into this.

Please read the discussion on the v3 group about modifying the object prototype - https://groups.google.com/forum/#!topic/google-maps-js-api-v3/sLnpnZdKklY

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