TC39 pipeline operator

JavaScript has come a long way. What started as a simple scripting language now powers complex web applications, backend servers, mobile apps, and even desktop software. As JavaScript has evolved, so has the complexity of the code developers write every day.

One common challenge is dealing with long chains of nested function calls. These chains are often difficult to read. Even experienced developers sometimes find debugging frustrating. This is where the TC39 Pipeline Operator comes in. 

The pipeline operator improves readability by clearly showing how data flows from one step to the next. Instead of nesting function calls, it allows developers to write logic as a clean, sequential series of operations.

In this guide, we will explore what the pipeline operator is, why it matters, and how it can improve the way JavaScript code is written.

Let us get started.

 

What is the TC39 Pipeline Operator?

The pipeline operator is a proposed JavaScript feature. It allows the result of one expression to be passed into another expression in a clear, left-to-right sequence.

Consider this example without a pipeline:

sanitize(parse(map(loadInput())));

This code works, but it is not easy to read. You have to start from the innermost function and work your way outward. That extra mental effort slows understanding.

The pipeline operator solves this problem by making the flow of data explicit and sequential. Conceptually, it allows developers to write transformations as a series of steps, rather than nested calls.

In simple terms, it lets you write code as a series of clear, readable steps.

 

Code With & Without a Pipeline (Conceptual)

Code Without a Pipeline Operator:

 const result = formatCurrency(applyTax(discount(price)));

This works fine for small examples. But as the logic grows, nested function calls quickly become hard to follow.

 

Code With the Pipeline Operator

 const result = price

  |> discount

  |> applyTax

  |> formatCurrency;


Now the flow is clear. You can see exactly what happens to the data at each step. Each line represents a single operation, making the code easier to read, explain, and maintain.

 

Key Benefits of the Pipeline Operator

  • Better Readability: The code flows from top to bottom, just like normal reading. This makes it easier to understand what the code is doing at a glance.
  • Less Nesting: Nested function calls are difficult to track. Pipelines flatten the logic into simple steps, which reduces confusion.
  • Clear Data Flow: Each step represents a single transformation, making intent explicit.
  • Better Maintainability: Readable code is easier to maintain. New team members can understand the logic faster, and future changes are simpler to make.
  • Works Well With Functional Programming: The pipeline operator fits naturally with functional programming, where data moves through a series of small, focused functions.


Pipeline Styles: Hack vs F# (Background)

During the early development of the TC39 pipeline operator, different styles for passing values were considered. The two main styles were Hack-style and F#-style.

Hack-style uses a placeholder symbol (#) to show exactly where the value from the previous step should go in the next function. This makes it very flexible, especially for more complicated function calls.

F#-style is simpler. It automatically passes the piped value as the first argument of the next function. This is easier to read but is less flexible than Hack-style.

After careful discussion, TC39 chose Hack-style as the official design. F#-style was dropped and is not part of the current JavaScript pipeline operator proposal.


Current Status of the Pipeline Operator

The pipeline operator is still under discussion and has not been finalized.

Even so, many tools already support it through transpilers like Babel, making it possible to experiment with it today. 

Some practical use cases of Pipeline Operator at present include:

  • Data Transformation: It can process API or JSON data step by step in a readable flow.
  • Form Validation: Users can employ it to apply multiple input checks and cleanup functions in sequence.
  • Analytics & Logging: The operator can track and process events clearly without nested code.
  • Utility Functions: It can be used to perform chain helper functions like string or array operations effortlessly.


Challenges to Keep in Mind

  • Learning Curve: Developers who are new to functional programming may need time to get comfortable with pipelines.
  • Tooling Support: Because the feature is not standardized yet, it depends on transpilers like Babel.
  • Risk of Overuse: Pipelines are powerful, but they are not needed everywhere. Overusing them can reduce clarity instead of improving it.


Conclusion

The TC39 Pipeline Operator offers a cleaner and more readable way to write JavaScript. It shows how data flows through functions step by step, reduces nesting, and improves the overall developer experience. While it is still a proposal, it already has strong use cases and growing support.

For now, it is worth understanding the concept, experimenting with it using transpilers, and keeping an eye on its progress. Even if it takes time to become a standard, the pipeline operator has already influenced how developers think about writing clearer, more readable JavaScript.