Gulp Scripts Throw Error: throw new errors.AssertionError - gulp

Question

Assertion Error using Gulp:
$ gulp scripts
assert.js:42
throw new errors.AssertionError({
^
AssertionError [ERR_ASSERTION]: Task function must be specified
at Gulp.set [as _setTask] (/Users/ThedWord/Documents/my-project/node_modules/undertaker/lib/set-task.js:10:3)
at Gulp.task (/Users/ThedWord/Documents/my-proje
ct/node_modules/undertaker/lib/task.js:13:8)
at Object.<anonymous> (/Users/ThedWord/Documents/my-project/gulpfile.js:10:6)
at Module._compile (module.js:660:30)
at Object.Module._extensions..js (module.js:671:
at Module.load (module.js:573:32)
at tryModuleLoad (module.js:513:12)
at Function.Module._load (module.js:505:3)
at Module.require (module.js:604:17)
at require (internal/module.js:11:18)
/*eslint-env node */
const gulp = require('gulp');
const sass = require('gulp-sass');
const autoprefixer = require('gulp-autoprefixer');
const browserSync = require('browser-sync').create();
const eslint = require('gulp-eslint');
const jasmine = require('gulp-jasmine-phantom');
const concat = require('gulp-concat');
gulp.task('default', ['copy-html', 'copy-images', 'styles', 'lint'], function() {
gulp.watch('sass/**/*.scss', ['styles']);
gulp.watch('js/**/*.js', ['lint']);
gulp.watch('/index.html', ['copy-html']);
gulp.watch('./build/index.html').on('change', browserSync.reload);
});
browserSync.init({
server: './dist'
});
gulp.task('scripts', function(){
gulp.src('js/**/*.js')
.pipe(concat('all.js'))
.pipe(gulp.dest('dist/js'));
});
gulp.task('scripts-dist', function(){
gulp.src('js/**/*.js')
.pipe(concat('all.js'))
.pipe(gulp.dest('dist/js'));
});
gulp.task('copy-html', function() {
gulp.src('./index.html')
.pipe(gulp.dest('./dist'));
});
gulp.task('copy-images', function(){
gulp.src('img/*')
.pipe(gulp.dest('dist/img'));
});
gulp.task('styles', function() {
gulp.src('sass/**/*.scss')
.pipe(sass().on('error', sass.logError))
.pipe(autoprefixer({
browsers: ['last 2 versions']
}))
.pipe(gulp.dest('dist/css'))
.pipe(browserSync.stream());
});
gulp.task('lint', function () {
return gulp.src(['js/**/*.js'])
// eslint() attaches the lint output to the eslint property
// of the file object so it can be used by other modules.
.pipe(eslint())
// eslint.format() outputs the lint results to the console.
// Alternatively use eslint.formatEach() (see Docs).
.pipe(eslint.format())
// To have the process exit with an error code (1) on
// lint error, return the stream and pipe to failOnError last.
.pipe(eslint.failOnError());
});
gulp.task('dist', [
'copy-html',
'copy-images',
'styles',
'lint',
'scripts-dist'
]);
gulp.task('tests', function () {
gulp.src('tests/spec/extraSpec.js')
.pipe(jasmine({
integration: true,
vendor: 'js/**/*.js'
}));
});

Answer 1

The problem you are encountering is that you are running gulp v4.0 using gulp 3 syntax. The AssertionError: Task function must be specified error comes from the fact that gulp.task has changed and the 3 parameters signature was removed. In short, your task below will need to be changed to remove the [] parameter:
gulp.task('default', ['copy-html', 'copy-images', 'styles', 'lint'], function() {
gulp.watch('sass/**/*.scss', ['styles']);
gulp.watch('js/**/*.js', ['lint']);
gulp.watch('/index.html', ['copy-html']);
gulp.watch('./build/index.html').on('change', browserSync.reload);
});
This article will help you migrate to gulp 4 syntax.
If you'd like a simple fix to your problem, without having to make changes to your gulpfile.js, run the following command to downgrade your version of gulp from version 4 to 3.9.1:
npm install gulp#3.9.1 --save
Assuming all goes well you should no longer see the Assertion error.