Task dependencies in Gulp

Question

There is the following gulpfile.js

const { watch, src, dest, parallel, series } = require('gulp')
const uglify = require('gulp-uglify')
const browserSync = require('browser-sync').create()
const htmlMin = require('gulp-htmlmin')
const cleanCSS = require('gulp-clean-css')
const imagemin = require('gulp-imagemin')
const hash = require('gulp-hash')                   // !!!
const references = require('gulp-hash-references')  // !!!
const del = require('del')
const path = require('path')

const manifestFile = 'asset-manifest.json'
const buildDir = './build'

function serve() {
    browserSync.init({
        server: {
            baseDir: "./"
        }
    })
    watch("./*.html").on('change', browserSync.reload)
    watch("./css/**/*.css").on('change', browserSync.reload)
    watch("./**/*.js").on('change', browserSync.reload)
}

function buildHTML(cb) {
    src('index.html')
        .pipe(references(manifestFile)) // replace file paths in index.html according to the manifest
        .pipe(htmlMin({
            collapseWhitespace: true
        }))
        .pipe(dest(buildDir))
    cb()
}

function buildCSS(cb) {
    src('./css/**/*.css')
        .pipe(cleanCSS())
        .pipe(hash())
        .pipe(dest(path.join(buildDir, 'css')))
        .pipe(hash.manifest(manifestFile)) // generate a manifest file
        .pipe(dest('.'))
    cb()
}


function buildJS(cb) {
    src(['./**/*.js', '!./node_modules/**', '!./gulpfile.js'])
        .pipe(uglify())
        .pipe(hash())
        .pipe(dest('build/'))
        .pipe(hash.manifest(manifestFile)) // generate a manifest file
        .pipe(dest('.'))
    cb()
}

function buildImages(cb) {
    src('./img/**/*.png')
        .pipe(imagemin([
            imagemin.optipng({ optimizationLevel: 7 })
        ]))
        .pipe(dest(path.join(buildDir, 'img')))
    cb()
}


exports.build = series(buildJS, buildCSS, buildHTML) // !!!
exports.default = serve

I'm trying to hash *.css and *.js file names and replace their old names with hashed ones in the build/index.html file. But the problem is that the function "buildHTML" starts working earlier than the "asset-manifest.json" file created. What am I doing wrong?

Answer 1

You have to return the streams created by your functions to ensure that they run in the expected order and to catch any possible errors. No need to use a callback:

function buildHTML() {
    return src('index.html')
        .pipe(references(manifestFile)) // replace file paths in index.html according to the manifest
        .pipe(htmlMin({
            collapseWhitespace: true
        }))
        .pipe(dest(buildDir));
}

function buildCSS() {
    return src('./css/**/*.css')
        .pipe(cleanCSS())
        .pipe(hash())
        .pipe(dest(path.join(buildDir, 'css')))
        .pipe(hash.manifest(manifestFile)) // generate a manifest file
        .pipe(dest('.'));
}


function buildJS() {
    return src(['./**/*.js', '!./node_modules/**', '!./gulpfile.js'])
        .pipe(uglify())
        .pipe(hash())
        .pipe(dest('build/'))
        .pipe(hash.manifest(manifestFile)) // generate a manifest file
        .pipe(dest('.'));
}

function buildImages() {
    return src('./img/**/*.png')
        .pipe(imagemin([
            imagemin.optipng({ optimizationLevel: 7 })
        ]))
        .pipe(dest(path.join(buildDir, 'img')));
}