Task Function Must Be Specified: Explained

Task Function Must Be Specified: Explained

AssertionError [ERR_ASSERTION]: Task operate have to be specified happens resulting from conflicts between the syntaxes of gulp 3 and gulp 4.0. Although many of the syntax is similar for each variations, just a little distinction is sufficient to generate this error.Assertionerror Err Assertion Task Function Must Be Specified

But you don’t have to be harassed whereas seeing it in your display as a result of this put up will clarify the trigger and a number of options for the error into consideration intimately. This is why it is best to begin studying it now to repair the said error within the subsequent minute of finishing this text.

AssertionError [ERR_ASSERTION]: Task Function Must Be Specified: Causes

The AssertionError [ERR_ASSERTION]: Task operate have to be specified is prompted while you improve to gulp 4.0 whereas utilizing the code written for gulp 3. With the brand new model of gulp, some adjustments have been launched, which creates conflicts between the previous code and the brand new model.

– Using Gulp 3 Syntax in Gulp 4.0

If you’ve got not too long ago switched to gulp 4.0 and all of a sudden, the duty operate have to be specified error exhibits up in your display, there could be an issue with the syntax. The gulp 3 syntax isn’t solely the identical because the one in gulp 4.Why Is Assertionerror Err Assertion Task Function Must Be Specified

Specifically, the duty() operate accepts barely completely different arguments in gulp 4.0 than in gulp 3. For instance, you’re executing the duty() operate by passing a listing to it in gulp 4.0. In such a state of affairs, the identical error will happen as a result of the record parameter is deprecated in gulp 4.0.

For your comfort, we’re attaching a code snippet to see what isn’t acceptable in gulp 4.0.

gulp.activity(‘default’, [‘task1’, ‘task2’], operate() {…});

AssertionError [ERR_ASSERTION]: Task Function Must Be Specified: Fixes

You can repair the assertion error by working gulp.collection() or gulp.parallel() features as a substitute of the record parameter whereas executing the duty(). Also, you’ve got the choice to downgrade your present gulp model to three.9.1 to resolve the identical error nevertheless it’s not advisable.

– Go for the Gulp.collection() Function

It could be greatest to use the gulp.collection() operate to resolve the said error in gulp 4.0. The given operate will exchange the sq. brackets “[]” indicating a listing of duties. It will make sure that the duties handed to it are executed in a sequence.

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You should know that the gulp duties are asynchronous by nature, making them run parallel to one another. Thus, wrapping the duties in a listing received’t allow you to set their execution sequence. Here, the gulp.collection() operate comes with the additional good thing about working the duties in a sequence. You can name it the one which makes the gulp duties synchronous.

The upcoming code block will educate you methods to use the gulp.collection() operate to make issues work.

gulp.activity(‘default’, gulp.collection(‘task1’, ‘task2’, operate() {…}));

Here, some extent to notice is that you simply may get the assertionerror [err_assertion]: activity by no means outlined: after utilizing the gulp.collection() operate. The explanation for the said error will be the duty() execution adopted by the duty() definition.

It means that you’re attempting to execute a activity() earlier than it has been outlined. This state of affairs calls for carrying the code block that defines the duty() above the duty() execution assertion.

As a outcome, you’ll see the gulp activity by no means outlined error go away. Please be at liberty to match the sequence of your script to the one shared under to take care of accuracy.

  1. Define the duty together with an non-obligatory return assertion.
  2. Execute the duty through the use of gulp.collection() operate.

If you want clarification in regards to the appropriate definition of a gulp activity, then know which you can outline it by specifying the operate key phrase adopted by the duty title and parentheses.

Moreover, the next block of code will present you methods to create the duties and help you in utilizing the collection() operate within the easiest kind to execute the identical.

const { collection } = require(‘gulp’);

// defining the primary activity

operate myFunc1(cb) {

// calling a callback() operate



// defining one other activity

operate myFunc2(cb) {

// calling a callback operate



// utilizing exports.default to execute the duties by way of the collection() operate

exports.default = collection(myFunc1, myFunc2);

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A callback() operate is named contained in the duties within the above code snippet. However, you may skip it and supply a activity physique as per your alternative.

Plus, the explanation behind utilizing export.default as a substitute of the duty() operate is that exporting ought to be the first registration mechanism. But in conditions the place export doesn’t work, you need to use the duty() operate with no second thought.

– Let the Gulp.parallel() Function Show the Magic

The gulp.parallel() operate will let you run all of the duties in parallel in gulp 4.0. Eventually, you’ll be capable to remove the error talked about within the title. All that you simply’ll must do is to interchange the sq. brackets representing a listing with the gulp.parallel() operate.Assertionerror Err Assertion Task Function Must Be Specified Fixes

Therefore, in case you aren’t considering setting the sequence of the duties, the mentioned operate shall be adequate to take away the identical error out of your system. Its utilization has been proven under on your reference.

gulp.activity(‘default’, gulp.parallel(‘task1’, ‘task2’, operate() {…}));

Now, in case you get caught with the duty by no means outlined error, defining the duty() earlier than executing it will work right here too. Once you appropriate the sequence of activity() definition and activity() execution, the mentioned error shall be gone for the nice.

– Hop Back to Gulp 3.9.1

Although hopping again to the older variations isn’t advisable, it might probably make the assertion error go backstage. Hence, if for any cause, you don’t wish to make adjustments to your code, it will be useful to downgrade to gulp 3.9.1.

After downgrading to gulp 3.9.1, there received’t be any conflicts within the activity() execution syntax, and the given error shall be fastened. Running the “npm install gulp@3.9.1” command within the challenge’s folder will allow you to change your present gulp model to three.9.1.


1. Is It Possible To Run Gulp Task in VS Code?

Yes, you may run gulp activity in Visual Studio Code. Mostly, the editor detects a gulp activity mechanically. But it’s also possible to press F1 adopted by typing “run task” and hitting “Enter” to see the record of all accessible duties.

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Next, you may choose a activity of your alternative and press Enter to run the identical.

2. When Does the ReferenceError: Primordials Error Occurs?

The said reference error often happens while you attempt to use gulp 3 with Node.js 12. The given variations of gulp and Node.js aren’t appropriate with one another. Thus, you’ll must improve to gulp 4.0 or override graceful-fs to model ^4.2.10.

3. What Does the Did You Forget To Signal Async Completion Error Tell?

The talked about error assertion says that you simply didn’t inform gulp 4.0 in regards to the completion of your asynchronous duties. Note that gulp 4 wants an express sign that informs it in regards to the async completion. So, you may repair it by returning a stream, a promise, a baby course of, or an EventEmitter.

4. Why Does Gulp 3 Don’t Want an Explicit Signal for Async Completion?

Gulp 3 doesn’t require a transparent sign for async completion as a result of it assumes your synchronous activity with asynchronous code to be synchronous within the code. Eventually, it thinks that the duty is accomplished as soon as the duty operate returns and doesn’t demand express sign.


According to our analysis, the assertion error stating that the duty operate have to be specified pops up resulting from incorrect execution of the duty(). It has its trigger hidden behind the thought of fixing the duty() execution syntax in gulp 4.0. You can learn the details of this text right here:

  • You can repair the assertion error through the use of the gulp.collection() operate as a substitute of the record parameter.
  • It could be useful to run the gulp.parallel() operate as a substitute of the record parameter.
  • If you wish to use the record parameter for executing the duty(), it is best to use gulp 3.9.1.
  • It could be higher to tweak your code to make it work with the newer gulp model than downgrading gulp.

Now, you have to have understood that the given error just isn’t as sophisticated as its assertion as a result of you may remedy it by barely tweaking your code.


  • https://stackoverflow.com/questions/51098749/everytime-i-run-gulp-anything-i-get-a-assertion-error-task-function-must-be
  • https://gulpjs.com/docs/en/getting-started/creating-tasks/

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