Add capitalize() util.

lib/util.test.tsx

@@ -1,4 +1,5 @@
 import {
+  capitalize,
   flatten,
   float,
   inclusiveRange,
@@ -51,3 +52,10 @@ test("toFriendlyDecimal() works", () => {
 test("withoutNulls() works", () => {
   expect(withoutNulls([1, 2, 0, null, 3])).toEqual([1, 2, 0, 3]);
 });
+
+test("capitalize() works", () => {
+  for (let boop of ["boop", "BOOP", "Boop", "bOoP"]) {
+    expect(capitalize(boop)).toBe("Boop");
+  }
+  expect(capitalize("")).toBe("");
+});

lib/util.ts

@@ -132,3 +132,11 @@ export function withoutNulls<T>(arr: (T | null)[]): T[] {
 export function lerp(a: number, b: number, amount: number) {
   return a + amount * (b - a);
 }
+
+/**
+ * Capitalize the given word, forcing the first letter to
+ * uppercase and the rest to lowercase.
+ */
+export function capitalize(value: string) {
+  return value.slice(0, 1).toUpperCase() + value.slice(1).toLowerCase();
+}