diff --git a/src/components/binsearch.js b/src/components/binsearch.js
new file mode 100644
index 000000000..5989b6fb2
--- /dev/null
+++ b/src/components/binsearch.js
@@ -0,0 +1,48 @@
+"use strict";
+exports.__esModule = true;
+function binsearch_helper(arr, start, end, v, comparator) {
+    //    console.log("binsearch_helper: " + start + ", " + end + ", comparing against " + v);
+    if (start >= end) {
+        return -1; // not found
+    }
+    var midpoint = Math.floor((start + end) / 2);
+    //    console.log("midpoint = " + midpoint);
+    // Find the earliest matching index.
+    var comparison = comparator(arr[midpoint], v);
+    //    if ((arr[midpoint] === v) && ((midpoint === 0) || (arr[midpoint-1] != v))) {
+    if (comparison === 0) {
+        //	console.log("A");
+        // Found it. Is it the earliest one?
+        if ((midpoint === 0) || (comparator(arr[midpoint - 1], v) != 0)) {
+            return midpoint;
+        }
+    }
+    if (comparison < 0) {
+        //	console.log("B");
+        return binsearch_helper(arr, midpoint + 1, end, v, comparator);
+    }
+    else {
+        //	console.log("C");
+        return binsearch_helper(arr, start, midpoint - 1, v, comparator);
+    }
+}
+// Find the index of the earliest occurrence of v in arr using binary search.
+// Return -1 if not found.
+function binsearch(arr, v, comparator) {
+    if (comparator === void 0) { comparator = undefined; }
+    if (typeof comparator === "undefined") {
+        //	console.log("undefined");
+        comparator = (function (a, b) {
+            console.log("Comparing " + JSON.stringify(a) + " to " + JSON.stringify(b));
+            if (a === b) {
+                return 0;
+            }
+            if (a < b) {
+                return -1;
+            }
+            return 1;
+        });
+    }
+    return binsearch_helper(arr, 0, arr.length, v, comparator);
+}
+exports.binsearch = binsearch;
diff --git a/src/components/binsearch.ts b/src/components/binsearch.ts
new file mode 100644
index 000000000..ad9751a80
--- /dev/null
+++ b/src/components/binsearch.ts
@@ -0,0 +1,50 @@
+type ComparatorType<T> = (arg1: T, arg2: T) => number;
+
+function binsearch_helper<T>(arr: Array<T>,
+			     start: number,
+			     end: number,
+			     v: T,
+			     comparator: ComparatorType<T>) : number {
+//    console.log("binsearch_helper: " + start + ", " + end + ", comparing against " + v);
+    if (start >= end) {
+	return -1; // not found
+    }
+    let midpoint = Math.floor((start + end) / 2);
+//    console.log("midpoint = " + midpoint);
+    // Find the earliest matching index.
+    let comparison = comparator(arr[midpoint], v);
+    //    if ((arr[midpoint] === v) && ((midpoint === 0) || (arr[midpoint-1] != v))) {
+    if (comparison === 0) {
+//	console.log("A");
+	// Found it. Is it the earliest one?
+	if ((midpoint === 0) || (comparator(arr[midpoint-1], v) != 0)) {
+	    return midpoint;
+	}
+    }
+    if (comparison < 0) {
+//	console.log("B");
+	return binsearch_helper(arr, midpoint+1, end, v, comparator);
+    } else {
+//	console.log("C");
+	return binsearch_helper(arr, start, midpoint-1, v, comparator);
+    }
+}
+
+// Find the index of the earliest occurrence of v in arr using binary search.
+// Return -1 if not found.
+export function binsearch<T>(arr: Array<T>, v: T, comparator : ComparatorType<T> = undefined) {
+    if (typeof comparator === "undefined") {
+//	console.log("undefined");
+	comparator = ((a, b) => {
+	    console.log("Comparing " + JSON.stringify(a) + " to " + JSON.stringify(b));
+	    if (a === b) {
+		return 0;
+	    }
+	    if (a < b) {
+		return -1;
+	    }
+	    return 1;
+	});
+    }
+    return binsearch_helper(arr, 0, arr.length, v, comparator);
+}