Merge from gist: cross-browser compatibility, fallback on nophoto url…

…, handle U-prefixed matric numbers

IVLE photos/classmate-photos.js

@@ -10,35 +10,48 @@
 
 // Credits: Camillus Cai for the full matric number function
 
-var normalize = function (id) {
-  var matches = id.toUpperCase().match(/^A\d{7}|U\d{6,7}/);
-  if (matches) {
-    var match = matches[0];
-    if (match[0] === 'U' && match.length === 8) {
-      match = match.slice(0, 3) + match.slice(4);
-    }
-    var weights = {
-      U: [0, 1, 3, 1, 2, 7],
-      A: [1, 1, 1, 1, 1, 1]
-    }[match[0]];
-    for (var i = 0, sum = 0, digits = match.slice(-6); i < 6; i++) {
-      sum += weights[i] * digits[i];
-    }
-    return match + 'YXWURNMLJHEAB'[sum % 13];
-  }
-};
-
-var nopics = document.evaluate('//img[@src="/images/nophoto.jpg" and @id]', document, null, 6, null);
-for (var i = 0; i < nopics.snapshotLength; i++) {
-  var fullMatric = normalize(nopics.snapshotItem(i).id);
-  if (fullMatric) {
-    var img = nopics.snapshotItem(i);
-    img.onerror = function () {
-      var next = {'U':'P', 'P':'X', 'X':null}[this.src.slice(-1)];
-      if (next) {
-        this.src = this.src.slice(0, -1) + next;
-      }
+(function () {
+    var calculateNUSMatricNumber = function (id) {
+        var matches = id.toUpperCase().match(/^A\d{7}|U\d{6,7}/);
+        if (matches) {
+            var match = matches[0];
+
+            // Discard 3rd digit from U-prefixed NUSNET ID
+            if (match[0] === 'U' && match.length === 8) {
+                match = match.slice(0, 3) + match.slice(4);
+            }
+
+            var weights = {
+                U: [0, 1, 3, 1, 2, 7],
+                A: [1, 1, 1, 1, 1, 1]
+            }[match[0]];
+
+            for (var i = 0, sum = 0, digits = match.slice(-6); i < 6; i++) {
+                sum += weights[i] * digits[i];
+            }
+
+            return match + 'YXWURNMLJHEAB'[sum % 13];
+        }
     };
-    img.src = 'https://mysoc.nus.edu.sg/mysoc/images/stdphoto.php?matric=' + fullMatric + '&type=U';
-  }
-}
+
+    var PHOTO_URL = 'https://mysoc.nus.edu.sg/mysoc/images/stdphoto.php?matric=';
+    var NOPHOTO_URL = 'https://ivle.nus.edu.sg/images/nophoto.jpg';
+    var TYPES = ['U', 'P', 'X'];
+
+    var imgs = document.getElementsByTagName('img');
+    for (var i = 0; i < imgs.length; i++) {
+        var img = imgs[i];
+        if (img.id && img.src === NOPHOTO_URL) {
+            var matricNumber = calculateNUSMatricNumber(img.id);
+            if (matricNumber) {
+                (function () {
+                    var typeIndex = 0;
+                    img.onerror = function () {
+                        this.src = typeIndex < TYPES.length ? PHOTO_URL + matricNumber + '&type=' + TYPES[typeIndex++] : NOPHOTO_URL;
+                    }
+                    img.onerror.call(img);
+                })();
+            }
+        }
+    }
+})();