NodeJS – Gulp – AssertionError [ERR_ASSERTION] – Fix

While migrating from Gulp 3.x to Gulp 4.x, these are some AssertionError errors we may getting:


  • AssertionError [ERR_ASSERTION]: Task function must be specified
  • AssertionError [ERR_ASSERTION]: Task never defined:
  • The following tasks did not complete: Did you forget to signal async completion?

How to Fix Assertion Error?

Here are few points to take care task definition and execution:

  1. First define task
  2. Use return
  3. Then execute with gulp.series()

Here, is the quick Gulp code which is working with Gulp v4:

// First define task with Return
gulp.task('css-minify', function () {
    return gulp.src('assets/images/*.*')
        .pipe(smushit({verbose: true}))

// Then execute task with bracket '()' instead of '[]'
gulp.task('default', gulp.series('css-minify'));

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