Move zeroPad function to BaseTypes and add tests for it

lib/OpenLayers/BaseTypes.js

@@ -295,7 +295,25 @@ OpenLayers.Number = {
             str = integer + dsep + rem;
         }
         return str;
-    }
+    },
+
+    /**
+     * Method: zeroPad
+     * Create a zero padded string optionally with a radix for casting numbers.
+     *
+     * Parameters:
+     * num - {Number} The number to be zero padded.
+     * len - {Number} The length of the string to be returned.
+     * radix - {Number} An integer between 2 and 36 specifying the base to use
+     *     for representing numeric values.
+     */
+    zeroPad: function(num, len, radix) {
+        var str = num.toString(radix || 10);
+        while (str.length < len) {
+            str = "0" + str;
+        }
+        return str;
+    }    
 };
 
 /**

tests/BaseTypes.html

@@ -278,6 +278,17 @@
         OpenLayers.Number.decimalSeparator = ",";
         t.eq(format(num, 3), "12.345,679", "changing thousands/decimal separator globally works");
     }
+    
+    function test_Number_zeroPad(t) {
+        t.plan(6);
+        var pad = OpenLayers.Number.zeroPad;
+        t.eq(pad(15, 4), "0015", "left padding works");
+        t.eq(pad(15, 2), "15", "no left padding when equal to number of digits");
+        t.eq(pad(15, 1), "15", "no left padding when less than number of digits");
+        t.eq(pad(10, 5, 2), "01010", "radix modified and padding works");
+        t.eq(pad(10, 5, 8), "00012", "radix modified and padding works");
+        t.eq(pad(10, 5, 36), "0000a", "radix modified and padding works");
+    }
 
     function test_Function_bind(t) {
         t.plan(12);