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// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
import { stringify } from "./stringify.ts";
/** Options for {@linkcode CsvStringifyStream}. */
export interface CsvStringifyStreamOptions {
/**
* Delimiter used to separate values.
*
* @default {","}
*/
readonly separator?: string;
/**
* A list of columns to be included in the output.
*
* If you want to stream objects, this option is required.
*
* @default {[]}
*/
readonly columns?: Array<string>;
}
/**
* Convert each chunk to a CSV record.
*
* @example Write CSV to a file
* ```ts
* import { CsvStringifyStream } from "@std/csv/stringify-stream";
* import { assertEquals } from "@std/assert/equals";
*
* async function writeCsvToTempFile(): Promise<string> {
* const path = await Deno.makeTempFile();
* using file = await Deno.open(path, { write: true });
*
* const readable = ReadableStream.from([
* { id: 1, name: "one" },
* { id: 2, name: "two" },
* { id: 3, name: "three" },
* ]);
*
* await readable
* .pipeThrough(new CsvStringifyStream({ columns: ["id", "name"] }))
* .pipeThrough(new TextEncoderStream())
* .pipeTo(file.writable);
*
* return path;
* }
*
* const path = await writeCsvToTempFile();
* const content = await Deno.readTextFile(path);
* assertEquals(content, "id,name\r\n1,one\r\n2,two\r\n3,three\r\n");
* ```
*
* @example Write TSV to a file
* ```ts
* import { CsvStringifyStream } from "@std/csv/stringify-stream";
* import { assertEquals } from "@std/assert/equals";
*
* async function writeTsvToTempFile(): Promise<string> {
* const path = await Deno.makeTempFile();
* using file = await Deno.open(path, { write: true });
*
* const readable = ReadableStream.from([
* { id: 1, name: "one" },
* { id: 2, name: "two" },
* { id: 3, name: "three" },
* ]);
*
* await readable
* .pipeThrough(
* new CsvStringifyStream({
* columns: ["id", "name"],
* separator: "\t",
* }),
* )
* .pipeThrough(new TextEncoderStream())
* .pipeTo(file.writable);
*
* return path;
* }
*
* const path = await writeTsvToTempFile();
* const content = await Deno.readTextFile(path);
* assertEquals(content, "id\tname\r\n1\tone\r\n2\ttwo\r\n3\tthree\r\n");
* ```
*
* @typeParam TOptions The type of options for the stream.
*/
export class CsvStringifyStream<TOptions extends CsvStringifyStreamOptions>
extends TransformStream<
TOptions["columns"] extends Array<string> ? Record<string, unknown>
: Array<unknown>,
string
> {
/**
* Construct a new instance.
*
* @param options Options for the stream.
*/
constructor(options?: TOptions) {
const { separator, columns = [] } = options ?? {};
super(
{
start(controller) {
if (columns && columns.length > 0) {
try {
controller.enqueue(
stringify(
[columns],
separator !== undefined
? { separator, headers: false }
: { headers: false },
),
);
} catch (error) {
controller.error(error);
}
}
},
transform(chunk, controller) {
try {
controller.enqueue(
stringify(
[chunk],
separator !== undefined
? { separator, headers: false, columns }
: { headers: false, columns },
),
);
} catch (error) {
controller.error(error);
}
},
},
);
}
}
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