Perf: faster string[] join

Build/lib/misc.ts

@@ -1 +1,18 @@
 export const isTruthy = <T>(i: T | 0 | '' | false | null | undefined): i is T => !!i;
+
+export const fastStringArrayJoin = (arr: string[], sep: string) => {
+  let result = '';
+  for (let i = 0, len = arr.length; i < len; i++) {
+    if (i !== 0) {
+      result += sep;
+    }
+    result += arr[i];
+  }
+  return result;
+};
+
+export const fastStringArrayJoin2 = (arr: string[], sep: string) => {
+  return arr.reduce((acc, cur, index) => {
+    return index === 0 ? cur : acc + sep + cur;
+  }, '');
+};