Add joinAtMost utility function

Author: mbg

src/util.test.ts

@@ -539,3 +539,27 @@ test("checkDiskUsage succeeds and produces positive numbers", async (t) => {
     t.true(diskUsage.numTotalBytes > 0);
   }
 });
+
+test("joinAtMost - behaves like join if limit is <= 0", (t) => {
+  const sep = ", ";
+  const array: string[] = new Array(10).fill("test");
+  t.is(util.joinAtMost(array, sep, 0), array.join(sep));
+  t.is(util.joinAtMost(array, sep, -1), array.join(sep));
+});
+
+test("joinAtMost - behaves like join if limit is >= the size of the array", (t) => {
+  const sep = ", ";
+  const array: string[] = new Array(10).fill("test");
+  t.is(util.joinAtMost(array, sep, 10), array.join(sep));
+  t.is(util.joinAtMost(array, sep, 11), array.join(sep));
+});
+
+test("joinAtMost - truncates list if array is > than limit", (t) => {
+  const sep = ", ";
+  const array: string[] = Array.from(new Array(10), (_, i) => `test${i + 1}`);
+  const result = util.joinAtMost(array, sep, 5);
+  t.not(result, array.join(sep));
+  t.assert(result.endsWith(", ..."));
+  t.assert(result.includes("test5"));
+  t.false(result.includes("test6"));
+});

src/util.ts

@@ -1270,3 +1270,25 @@ export enum CleanupLevel {
   Clear = "clear",
   Overlay = "overlay",
 }
+
+/**
+ * Like `join`, but limits the number of elements that are joined together to `limit`
+ * and appends `...` if the limit is exceeded.
+ *
+ * @param array The array to join.
+ * @param separator The separator to join the array with.
+ * @param limit The maximum number of elements from `array` to join.
+ * @returns The result of joining at most `limit`-many elements from `array`.
+ */
+export function joinAtMost(
+  array: string[],
+  separator: string,
+  limit: number,
+): string {
+  if (limit > 0 && array.length > limit) {
+    array = array.slice(0, limit);
+    array.push("...");
+  }
+
+  return array.join(separator);
+}