template-replace-stream

template-replace-stream

A high performance {{ template }} replace stream working on binary or string streams.

This module is written in pure TypeScript and consists of only 252 lines of code.

Install

npm install template-replace-stream

Usage

You create a TemplateReplaceStream by passing a source of template variables and their replacement values to the constructor. This may either be a map containing key-value pairs, or a function that returns a replacement value for a given template string.

JavaScript

const {TemplateReplaceStream} = require("template-replace-stream");
const fs = require("node:fs");
const path = require("node:path");

// create a map of variables to replace. This will replace "{{replace-me}}" with "really fast"
const variables = new Map([["replace-me", "really fast"]]);

// create the streams
const readStream = fs.createReadStream(path.join(__dirname, "template.txt"));
const writeStream = fs.createWriteStream(path.join(__dirname, "example.txt"));
const templateReplaceStream = new TemplateReplaceStream(variables);

// connect the streams and put the template replace stream in the middle
readStream.pipe(templateReplaceStream).pipe(writeStream);
writeStream.on("finish", () => console.log("Finished writing example.txt"));

TypeScript

import {TemplateReplaceStream} from "template-replace-stream";
import fs from "node:fs";
import path from "node:path";

// create a map of variables to replace. This will replace "{{replace-me}}" with "really fast"
const variables = new Map([["replace-me", "really fast"]]);

// create the streams
const readStream = fs.createReadStream(path.join(__dirname, "template.txt"));
const writeStream = fs.createWriteStream(path.join(__dirname, "example.txt"));
const templateReplaceStream = new TemplateReplaceStream(variables);

// connect the streams and put the template replace stream in the middle
readStream.pipe(templateReplaceStream).pipe(writeStream);
writeStream.on("finish", () => console.log("Finished writing example.txt"));

Advanced

Readable Stream as Replacement Value Source

It's also possible to pass another Readable as replacement value source to the TemplateReplaceStream. In fact, the README you are just reading was created using this feature. This makes it possible to replace template variables with whole files without reading them into a stream before.

Advanced Example Code

import {StringSource, TemplateReplaceStream} from "template-replace-stream";
import fs from "fs";
import path from "path";
import sloc from "sloc"

const rootDir = path.join(__dirname, "..");
const exampleFiles = ["javascript-example.js", "typescript-example.ts", "create-readme.ts"];

const loc = sloc(fs.readFileSync(path.join(rootDir, "src", "template-replace-stream.ts"), "utf8"), "ts").total;

/**
 * Opens a file stream and replaces the import paths in the examples. This is used to
 * have module imports in the README but still local imports in the examples.
 *
 * @param file The file to read.
 */
function openExampleStream(file: string) {
  const replaceStream = new TemplateReplaceStream(
      new Map([
        [`../src`, `"template-replace-stream"`],
        [`../dist`, `"template-replace-stream"`]
      ]),
      {
        startPattern: '"',
        endPattern: '"'
      }
  );
  return fs.createReadStream(path.join(__dirname, file)).pipe(replaceStream);
}

// the map of example files and their read streams and further template variables
const templateMap = new Map<string, StringSource>(exampleFiles.map((file) => [file, openExampleStream(file)]));
templateMap.set("loc", loc.toString());

// create the streams
const readmeReadStream = fs.createReadStream(path.join(rootDir, "README.template.md"));
const readmeWriteStream = fs.createWriteStream(path.join(rootDir, "README.md"));

// connect the streams and put the template replace stream in the middle
readmeReadStream.pipe(new TemplateReplaceStream(templateMap)).pipe(readmeWriteStream);
readmeWriteStream.on("finish", () => console.log("Finished writing README.md"));

Options

type TemplateReplaceStreamOptions = {
  /** Default: `false`. If true, the stream creates logs on debug level */
  log: boolean;
  /** Default: `false`. If true, the stream throws an error when a variable is missing */
  throwOnMissingVariable: boolean;
  /** Default: `100`. The maximum length of a variable name including whitespaces around it */
  maxVariableNameLength: number;
  /** Default: `'{{'`. The start pattern of a variable either as string or buffer */
  startPattern: string | Buffer;
  /** Default: `'}}'`. The end pattern of a variable either as string or buffer */
  endPattern: string | Buffer;
  /** The options for the lower level {@link Transform} stream. Do not replace transform or flush */
  streamOptions?: TransformOptions;
}