diff --git a/openlibrary/plugins/openlibrary/js/index.js b/openlibrary/plugins/openlibrary/js/index.js
index b9445ccc07f0..ce105dd33dba 100644
--- a/openlibrary/plugins/openlibrary/js/index.js
+++ b/openlibrary/plugins/openlibrary/js/index.js
@@ -10,7 +10,7 @@ import loadStyle from './loadStyle';
 import { ungettext, ugettext,  sprintf } from './i18n';
 import { addFadeInFunctionsTojQuery } from './jquery.others';
 import jQueryRepeat from './jquery.repeat';
-import { ForLoop, enumerate, htmlquote, websafe, foreach, join, len, range } from './jsdef';
+import { enumerate, htmlquote, websafe, foreach, join, len, range } from './jsdef';
 // Note this import will also load various jQuery plugins.
 // (jQuery.ScrollTo, jquery.hoverIntent, jquery.dataTables, dataTableExt,
 // highlight, removeHighlight, jTruncate, columnize)
@@ -59,7 +59,6 @@ window._uggettext = ugettext;
 
 window.Browser = Browser;
 window.Carousel = Carousel;
-window.ForLoop = ForLoop;
 window.Subject = Subject;
 window.Template = Template;
 
diff --git a/openlibrary/plugins/openlibrary/js/jsdef.js b/openlibrary/plugins/openlibrary/js/jsdef.js
index 65ef14b73954..4764c5c31d95 100644
--- a/openlibrary/plugins/openlibrary/js/jsdef.js
+++ b/openlibrary/plugins/openlibrary/js/jsdef.js
@@ -131,10 +131,10 @@ export function websafe(value) {
 export function htmlquote(text) {
     // This code exists for compatibility with template.js
     text = String(text);
-    text = text.replace("&", "&"); // Must be done first!
-    text = text.replace("<", "&lt;");
-    text = text.replace(">", "&gt;");
-    text = text.replace("'", "&#39;");
-    text = text.replace('"', "&quot;");
+    text = text.replace(/&/g, "&amp;"); // Must be done first!
+    text = text.replace(/</g, "&lt;");
+    text = text.replace(/>/g, "&gt;");
+    text = text.replace(/'/g, "&#39;");
+    text = text.replace(/"/g, "&quot;");
     return text;
 }
diff --git a/openlibrary/plugins/openlibrary/js/python.js b/openlibrary/plugins/openlibrary/js/python.js
index 58458bdd3199..e1dd10379c5e 100644
--- a/openlibrary/plugins/openlibrary/js/python.js
+++ b/openlibrary/plugins/openlibrary/js/python.js
@@ -1,4 +1,12 @@
 // used in templates/admin/index.html
+
+/**
+ * Add commas to a number
+ * e.g. 1000 becomes 1,000
+ * 1 million becomes 1,000,000
+ * @param {mixed} n
+ * @return {string}
+ */
 export function commify(n) {
     var text = n.toString();
     var re = /(\d+)(\d{3})/;
diff --git a/package.json b/package.json
index dea3a715bb5e..e519ed59ce03 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,7 @@
     "svg-min": "svgo static/images/**/*.svg && svgo static/images/*.svg",
     "lint:fix": "stylelint --syntax less --fix static/css/",
     "lint:js": "eslint --config .eslintrc.json .",
+    "test:unit": "jest --testRegex tests/unit/**/*.js",
     "test": "npm run check-bundles && stylelint --syntax less static/css/ && npm run lint:js"
   },
   "bundlesize": [
@@ -62,6 +63,7 @@
     "bundlesize": "^0.17.0",
     "detect-libc": "^1.0.3",
     "eslint": "^5.7.0",
+    "jest": "^24.5.0",
     "less": "^3.8.1",
     "node-gyp": "^3.8.0",
     "prebuild-install": "^5.2.1",
@@ -70,5 +72,19 @@
     "svgo": "1.1.1",
     "webpack": "4.27.1",
     "webpack-cli": "3.1.2"
+  },
+  "jest": {
+    "collectCoverageFrom": [
+      "openlibrary/plugins/openlibrary/js/**/*.js"
+    ],
+    "coverageThreshold": {
+      "global": {
+        "branches": 0.6,
+        "functions": 1,
+        "lines": 1,
+        "statements": 1
+      }
+    },
+    "collectCoverage": true
   }
 }
diff --git a/tests/unit/.eslintrc.json b/tests/unit/.eslintrc.json
new file mode 100644
index 000000000000..ffd805fdd463
--- /dev/null
+++ b/tests/unit/.eslintrc.json
@@ -0,0 +1,10 @@
+{
+  "env": {
+    "es6": true,
+    "jest": true
+  },
+  "globals": {
+    "test": true,
+    "expect": true
+  }
+}
diff --git a/tests/unit/js/test.jsdef.js b/tests/unit/js/test.jsdef.js
new file mode 100644
index 000000000000..d6631688b51c
--- /dev/null
+++ b/tests/unit/js/test.jsdef.js
@@ -0,0 +1,57 @@
+import { foreach, range, join, len, htmlquote, enumerate,
+    websafe } from '../../../openlibrary/plugins/openlibrary/js/jsdef';
+
+test('jsdef: python range function', () => {
+    expect(range(2, 5)).toEqual([2, 3, 4]);
+    expect(range(5)).toEqual([0, 1, 2, 3, 4]);
+    expect(range(0, 10, 2)).toEqual([0, 2, 4, 6, 8]);
+});
+
+test('jsdef: enumerate', () => {
+    expect(enumerate([1, 2, 3])).toEqual([
+        ['0', 1],
+        ['1', 2],
+        ['2', 3]
+    ]);
+});
+
+test('jsdef: foreach', () => {
+    let called = 0;
+    const loop = [];
+    const listToLoop = [1, 2, 3];
+    expect.assertions(1);
+    return new Promise((resolve) => {
+        foreach(listToLoop, loop, function (val, i) {
+            called += 1;
+            if (called === 3) {
+                expect(called).toBe(3);
+                resolve();
+            }
+        })
+    });
+});
+
+test('jsdef: join', () => {
+    const str = '-';
+    const joinFn = join.bind(str);
+    expect(joinFn(['1', '2'])).toBe('1-2');
+});
+
+test('jsdef: len', () => {
+    expect(len(['1', '2'])).toBe(2);
+});
+
+test('jsdef: htmlquote', () => {
+    expect(htmlquote(5)).toBe('5');
+    expect(htmlquote('<foo>')).toBe('&lt;foo&gt;');
+    expect(htmlquote('\'foo\': "bar"')).toBe('&#39;foo&#39;: &quot;bar&quot;');
+    expect(htmlquote('a&b')).toBe('a&amp;b');
+});
+
+test('jsdef: websafe', () => {
+    expect(websafe('<script>')).toBe('&lt;script&gt;');
+    // not sure if these are really necessary, but they document the current behaviour
+    expect(websafe(undefined)).toBe('');
+    expect(websafe(null)).toBe('');
+    expect(websafe({toString: undefined})).toBe('');
+});
diff --git a/tests/unit/js/test.python.js b/tests/unit/js/test.python.js
new file mode 100644
index 000000000000..b82aaea9a850
--- /dev/null
+++ b/tests/unit/js/test.python.js
@@ -0,0 +1,9 @@
+import { commify } from '../../../openlibrary/plugins/openlibrary/js/python';
+
+test( 'commify', () => {
+    expect(commify('5443232')).toBe('5,443,232');
+    expect(commify('50')).toBe('50');
+    expect(commify('5000')).toBe('5,000');
+    expect(commify(['1','2','3','45'])).toBe('1,2,3,45');
+    expect(commify([1, 20, 3])).toBe('1,20,3');
+} );
\ No newline at end of file