Refactoring

src/functions/join.ts

@@ -0,0 +1,31 @@
+import { Transform } from "stream";
+import { StringDecoder } from "string_decoder";
+import { WithEncoding } from "./baseDefinitions";
+/**
+ * Return a ReadWrite stream that joins streamed chunks using the given separator
+ * @param separator Separator to join with
+ * @param options
+ * @param options.encoding Encoding written chunks are assumed to use
+ */
+export function join(
+    separator: string,
+    options: WithEncoding = { encoding: "utf8" },
+): Transform {
+    let isFirstChunk = true;
+    const decoder = new StringDecoder(options.encoding);
+    return new Transform({
+        readableObjectMode: true,
+        async transform(chunk: Buffer, encoding, callback) {
+            const asString = decoder.write(chunk);
+            // Take care not to break up multi-byte characters spanning multiple chunks
+            if (asString !== "" || chunk.length === 0) {
+                if (!isFirstChunk) {
+                    this.push(separator);
+                }
+                this.push(asString);
+                isFirstChunk = false;
+            }
+            callback();
+        },
+    });
+}