Gulp-windowed NPM

Install

$ npm i gulp-windowed

Usage

The following example concatenates groups of 5 markdown files. If src/posts contains files post0.md through post99.md, then the next pipe would receive a stream containing page0.md through page19.md, where page0.md is the concatenation of post0.md through post4.md. The ordering is guaranteed by the use of gulp-sort.

import gulp from 'gulp'
import sort from 'gulp-sorted'
import { windowed } from 'gulp-windowed'
import concat from 'gulp-concat'

const run = () =>
  gulp
    .src('src/posts/*.md') // Posts in markdown
    .pipe(sort()) // Sorted by filename
    .pipe(
      windowed(
        5,
        (
          files,
          i // In groups of 5
        ) => files.pipe(concat(`page${i}.md`)) // Concatenated into one page where 'i' is the window number
      )
    ) // More pipes...

Here it is used to split groups of files into different folders:

import gulp from 'gulp'
import { windowed } from 'gulp-windowed'
import rename from 'gulp-rename'

const run = () =>
  gulp.src('src/*').pipe(
    windowed(10, (files, i, done) =>
      files.pipe(
        rename({
          dirname: `folder${i}`
        })
      )
    )
  ) // More pipes...

Here it is used to skip every other file:

import gulp from 'gulp'
import { windowed } from 'gulp-windowed'

const run = () =>
  gulp
    .src('src/*')
    .pipe(windowed(1, (files, i, done) => (i % 2 === 0 ? files : done()))) // More pipes...

Notice that the stream of File objects in the callback can be returned from the callback. They are subsequently written to the resulting stream for the next pipe outside the callback. This is useful because it allows you to perform stream operations on the groups of files, while also allowing you to merge the resulting streams back together to continue performing operations.

If you'd like an array of File objects instead of a stream then import and call arrayWindowed instead.

API

windowed(n, cb) -> DuplexObjectStream<File>

Calls cb with a readable object stream (or array for arrayWindowed) containing n vinyl File objects each time n are written to it. On stream end if there are any remaining File objects because the n threshold was not met then cb is called with a readable object stream (or array for arrayWindowed) containing the remaining [0, n) File objects. The contents of the duplex object stream returned by the method depends on cb (explained below).

Parameters:

n : int - A number of File objects to include per window. Must be a positive integer.
cb : (files, i, done) -> File | Array<File> | Promise<File | Array<File> | *> | Observable<File | Array<File> | *> | ChildProcess | ReadableObjectStream<File> | undefined - A callback which either calls done or returns a File object, an array of File objects, or an asynchronous operation in some returnable format (see possible cb return types and async-done). If an asynchronous operation is returned it will be resolved. If the result of cb, through calling done or returning an asynchronous operation, is a File object or an array of File objects then they will be written to the duplex object stream returned from windowed.
- files : ReadableObjectStream<File> | Array<File> - A readable object stream (or array for window.array) containing up to n vinyl File objects (see above from why not exactly n).
- i : int - The current zero-based window number (i.e. the number of times cb has been called minus one).
- done : (err, result) -> undefined - Call done(new Error(...)) for error or done(null, result) for success when performing asynchronous operations in non-returnable format or when performing strictly synchronous operations. This method does not need to be and should not be called if a valid value of the types mentioned above is returned from cb.