Refactoring with Codemods to Automate API Adjustments

Clear a Stale Characteristic Toggle

Let’s begin with a easy but sensible instance to reveal the
energy of codemods. Think about you’re utilizing a function
toggle in your
codebase to regulate the discharge of unfinished or experimental options.
As soon as the function is dwell in manufacturing and dealing as anticipated, the subsequent
logical step is to scrub up the toggle and any associated logic.

For example, think about the next code:

const information = featureToggle('feature-new-product-list') ? { title: 'Product' } : undefined;

As soon as the function is absolutely launched and not wants a toggle, this
might be simplified to:

const information = { title: 'Product' };

The duty entails discovering all cases of featureToggle within the
codebase, checking whether or not the toggle refers to
feature-new-product-list, and eradicating the conditional logic surrounding
it. On the identical time, different function toggles (like
feature-search-result-refinement, which can nonetheless be in improvement)
ought to stay untouched. The codemod must perceive the construction
of the code to use modifications selectively.

Understanding the AST

Earlier than we dive into writing the codemod, let’s break down how this
particular code snippet appears in an AST. You need to use instruments like AST
Explorer to visualise how supply code and AST
are mapped. It’s useful to grasp the node sorts you are interacting
with earlier than making use of any modifications.

The picture beneath reveals the syntax tree by way of ECMAScript syntax. It
incorporates nodes like Identifier (for variables), StringLiteral (for the
toggle title), and extra summary nodes like CallExpression and
ConditionalExpression.

Determine 2: The Summary Syntax Tree illustration of the function toggle verify

On this AST illustration, the variable information is assigned utilizing a
ConditionalExpression. The check a part of the expression calls
featureToggle('feature-new-product-list'). If the check returns true,
the consequent department assigns { title: 'Product' } to information. If
false, the alternate department assigns undefined.

For a process with clear enter and output, I want writing assessments first,
then implementing the codemod. I begin by defining a damaging case to
guarantee we don’t unintentionally change issues we need to go away untouched,
adopted by an actual case that performs the precise conversion. I start with
a easy situation, implement it, then add a variation (like checking if
featureToggle is known as inside an if assertion), implement that case, and
guarantee all assessments move.

This strategy aligns properly with Check-Pushed Growth (TDD), even
for those who don’t apply TDD usually. Understanding precisely what the
transformation’s inputs and outputs are earlier than coding improves security and
effectivity, particularly when tweaking codemods.

With jscodeshift, you possibly can write assessments to confirm how the codemod
behaves:

const rework = require("../remove-feature-new-product-list");

defineInlineTest(
  rework,
  {},
  `
  const information = featureToggle('feature-new-product-list') ? { title: 'Product' } : undefined;
  `,
  `
  const information = { title: 'Product' };
  `,
  "delete the toggle feature-new-product-list in conditional operator"
);

The defineInlineTest operate from jscodeshift means that you can outline
the enter, anticipated output, and a string describing the check’s intent.
Now, working the check with a standard jest command will fail as a result of the
codemod isn’t written but.

The corresponding damaging case would make sure the code stays unchanged
for different function toggles:

defineInlineTest(
  rework,
  {},
  `
  const information = featureToggle('feature-search-result-refinement') ? { title: 'Product' } : undefined;
  `,
  `
  const information = featureToggle('feature-search-result-refinement') ? { title: 'Product' } : undefined;
  `,
  "don't change different function toggles"
);

Writing the Codemod

Let’s begin by defining a easy rework operate. Create a file
known as rework.js with the next code construction:

module.exports = operate(fileInfo, api, choices) {
  const j = api.jscodeshift;
  const root = j(fileInfo.supply);

  // manipulate the tree nodes right here

  return root.toSource();
};

This operate reads the file right into a tree and makes use of jscodeshift’s API to
question, modify, and replace the nodes. Lastly, it converts the AST again to
supply code with .toSource().

Now we are able to begin implementing the rework steps:

1. Discover all cases of featureToggle.
2. Confirm that the argument handed is 'feature-new-product-list'.
3. Change the whole conditional expression with the consequent half,
   successfully eradicating the toggle.

Right here’s how we obtain this utilizing jscodeshift:

module.exports = operate (fileInfo, api, choices) {
  const j = api.jscodeshift;
  const root = j(fileInfo.supply);

  // Discover ConditionalExpression the place the check is featureToggle('feature-new-product-list')
  root
    .discover(j.ConditionalExpression, {
      check: {
        callee: { title: "featureToggle" },
        arguments: [{ value: "feature-new-product-list" }],
      },
    })
    .forEach((path) => {
      // Change the ConditionalExpression with the 'consequent'
      j(path).replaceWith(path.node.consequent);
    });

  return root.toSource();
};

The codemod above:

• Finds ConditionalExpression nodes the place the check calls
  featureToggle('feature-new-product-list').
• Replaces the whole conditional expression with the resultant (i.e., {
title: 'Product' }), eradicating the toggle logic and leaving simplified code
  behind.

This instance demonstrates how straightforward it’s to create a helpful
transformation and apply it to a big codebase, considerably decreasing
handbook effort.

You’ll want to jot down extra check instances to deal with variations like
if-else statements, logical expressions (e.g.,
!featureToggle('feature-new-product-list')), and so forth to make the
codemod strong in real-world eventualities.

As soon as the codemod is prepared, you possibly can check it out on a goal codebase,
such because the one you are engaged on. jscodeshift offers a command-line
instrument that you need to use to use the codemod and report the outcomes.

$ jscodeshift -t transform-name src/

After validating the outcomes, verify that each one practical assessments nonetheless
move and that nothing breaks—even for those who’re introducing a breaking change.
As soon as happy, you possibly can commit the modifications and lift a pull request as
a part of your regular workflow.

Codemods Enhance Code High quality and Maintainability

Codemods aren’t simply helpful for managing breaking API modifications—they will
considerably enhance code high quality and maintainability. As codebases
evolve, they typically accumulate technical debt, together with outdated function
toggles, deprecated strategies, or tightly coupled elements. Manually
refactoring these areas might be time-consuming and error-prone.

By automating refactoring duties, codemods assist hold your codebase clear
and freed from legacy patterns. Repeatedly making use of codemods means that you can
implement new coding requirements, take away unused code, and modernize your
codebase with out having to manually modify each file.

Refactoring an Avatar Element

Now, let’s take a look at a extra complicated instance. Suppose you’re working with
a design system that features an Avatar element tightly coupled with a
Tooltip. Each time a person passes a title prop into the Avatar, it
routinely wraps the avatar with a tooltip.

Determine 3: A avatar element with a tooltip

Right here’s the present Avatar implementation:

import { Tooltip } from "@design-system/tooltip";

const Avatar = ({ title, picture }: AvatarProps) => {
  if (title) {
    return (
      <Tooltip content material={title}>
        <CircleImage picture={picture} />
      </Tooltip>
    );
  }

  return <CircleImage picture={picture} />;
};

The objective is to decouple the Tooltip from the Avatar element,
giving builders extra flexibility. Builders ought to have the ability to resolve
whether or not to wrap the Avatar in a Tooltip. Within the refactored model,
Avatar will merely render the picture, and customers can apply a Tooltip
manually if wanted.

Right here’s the refactored model of Avatar:

const Avatar = ({ picture }: AvatarProps) => {
  return <CircleImage picture={picture} />;
};

Now, customers can manually wrap the Avatar with a Tooltip as
wanted:

import { Tooltip } from "@design-system/tooltip";
import { Avatar } from "@design-system/avatar";

const UserProfile = () => {
  return (
    <Tooltip content material="Juntao Qiu">
      <Avatar picture="/juntao.qiu.avatar.png" />
    </Tooltip>
  );
};

The problem arises when there are tons of of Avatar usages unfold
throughout the codebase. Manually refactoring every occasion can be extremely
inefficient, so we are able to use a codemod to automate this course of.

Utilizing instruments like AST Explorer, we are able to
examine the element and see which nodes characterize the Avatar utilization
we’re focusing on. An Avatar element with each title and picture props
is parsed into an summary syntax tree as proven beneath:

Determine 4: AST of the Avatar element utilization

Writing the Codemod

Let’s break down the transformation into smaller duties:

• Discover Avatar utilization within the element tree.
• Test if the title prop is current.
• If not, do nothing.
• If current:
• Create a Tooltip node.
• Add the title to the Tooltip.
• Take away the title from Avatar.
• Add Avatar as a toddler of the Tooltip.
• Change the unique Avatar node with the brand new Tooltip.

To start, we’ll discover all cases of Avatar (I’ll omit a few of the
assessments, however you must write comparability assessments first).

defineInlineTest(
    { default: rework, parser: "tsx" },
    {},
    `
    <Avatar title="Juntao Qiu" picture="/juntao.qiu.avatar.png" />
    `,
    `
    <Tooltip content material="Juntao Qiu">
      <Avatar picture="/juntao.qiu.avatar.png" />
    </Tooltip>
    `,
    "wrap avatar with tooltip when title is offered"
  );

Much like the featureToggle instance, we are able to use root.discover with
search standards to find all Avatar nodes:

root
  .discover(j.JSXElement, {
    openingElement: { title: { title: "Avatar" } },
  })
  .forEach((path) => {
    // now we are able to deal with every Avatar occasion
  });

Subsequent, we verify if the title prop is current:

root
  .discover(j.JSXElement, {
    openingElement: { title: { title: "Avatar" } },
  })
  .forEach((path) => {
    const avatarNode = path.node;

    const nameAttr = avatarNode.openingElement.attributes.discover(
      (attr) => attr.title.title === "title"
    );

    if (nameAttr) {
      const tooltipElement = createTooltipElement(
        nameAttr.worth.worth,
        avatarNode
      );
      j(path).replaceWith(tooltipElement);
    }
  });

For the createTooltipElement operate, we use the
jscodeshift API to create a brand new JSX node, with the title
prop utilized to the Tooltip and the Avatar
element as a toddler. Lastly, we name replaceWith to
exchange the present path.

Right here’s a preview of the way it appears in
Hypermod, the place the codemod is written on
the left. The highest half on the proper is the unique code, and the underside
half is the reworked end result:

Determine 5: Run checks inside hypermod earlier than apply it to your codebase

This codemod searches for all cases of Avatar. If a
title prop is discovered, it removes the title prop
from Avatar, wraps the Avatar inside a
Tooltip, and passes the title prop to the
Tooltip.

By now, I hope it’s clear that codemods are extremely helpful and
that the workflow is intuitive, particularly for large-scale modifications the place
handbook updates can be an enormous burden. Nevertheless, that is not the entire
image. Within the subsequent part, I’ll make clear a few of the challenges
and the way we are able to handle these less-than-ideal points.

Leveraging Supply Graphs and Check-Pushed Codemods

To deal with these complexities, codemods needs to be used alongside different
methods. For example, a couple of years in the past, I participated in a design
system elements rewrite challenge at Atlassian. We addressed this problem by
first looking out the supply graph, which contained the vast majority of inner
element utilization. This allowed us to grasp how elements have been used,
whether or not they have been imported underneath totally different names, or whether or not sure
public props have been ceaselessly used. After this search section, we wrote our
check instances upfront, guaranteeing we lined the vast majority of use instances, and
then developed the codemod.

In conditions the place we could not confidently automate the improve, we
inserted feedback or “TODOs” on the name websites. This allowed the
builders working the script to deal with particular instances manually. Often,
there have been solely a handful of such cases, so this strategy nonetheless proved
useful for upgrading variations.

Using Present Code Standardization Instruments

As you possibly can see, there are many edge instances to deal with, particularly in
codebases past your management—similar to exterior dependencies. This
complexity signifies that utilizing codemods requires cautious supervision and a
evaluate of the outcomes.

Nevertheless, in case your codebase has standardization instruments in place, similar to a
linter that enforces a specific coding fashion, you possibly can leverage these
instruments to cut back edge instances. By implementing a constant construction, instruments
like linters assist slim down the variations in code, making the
transformation simpler and minimizing surprising points.

For example, you would use linting guidelines to limit sure patterns,
similar to avoiding nested conditional (ternary) operators or implementing named
exports over default exports. These guidelines assist streamline the codebase,
making codemods extra predictable and efficient.

Moreover, breaking down complicated transformations into smaller, extra
manageable ones means that you can deal with particular person points extra exactly. As
we’ll quickly see, composing smaller codemods could make dealing with complicated
modifications extra possible.

Codemod Composition

Let’s revisit the function toggle removing instance mentioned earlier. Within the code snippet
we’ve got a toggle known as feature-convert-new must be eliminated:

import { featureToggle } from "./utils/featureToggle";

const convertOld = (enter: string) => {
  return enter.toLowerCase();
};

const convertNew = (enter: string) => {
  return enter.toUpperCase();
};

const end result = featureToggle("feature-convert-new")
  ? convertNew("Hey, world")
  : convertOld("Hey, world");

console.log(end result);

The codemod for take away a given toggle works tremendous, and after working the codemod,
we wish the supply to seem like this:

const convertNew = (enter: string) => {
  return enter.toUpperCase();
};

const end result = convertNew("Hey, world");

console.log(end result);

Nevertheless, past eradicating the function toggle logic, there are extra duties to
deal with:

• Take away the unused convertOld operate.
• Clear up the unused featureToggle import.

After all, you would write one huge codemod to deal with every little thing in a
single move and check it collectively. Nevertheless, a extra maintainable strategy is
to deal with codemod logic like product code: break the duty into smaller,
impartial items—similar to how you’ll usually refactor manufacturing
code.

Breaking It Down

We are able to break the large transformation down into smaller codemods and
compose them. The benefit of this strategy is that every transformation
might be examined individually, overlaying totally different instances with out interference.
Furthermore, it means that you can reuse and compose them for various
functions.

For example, you may break it down like this:

• A change to take away a particular function toggle.
• One other transformation to scrub up unused imports.
• A change to take away unused operate declarations.

By composing these, you possibly can create a pipeline of transformations:

import { removeFeatureToggle } from "./remove-feature-toggle";
import { removeUnusedImport } from "./remove-unused-import";
import { removeUnusedFunction } from "./remove-unused-function";

import { createTransformer } from "./utils";

const removeFeatureConvertNew = removeFeatureToggle("feature-convert-new");

const rework = createTransformer([
  removeFeatureConvertNew,
  removeUnusedImport,
  removeUnusedFunction,
]);

export default rework;

On this pipeline, the transformations work as follows:

1. Take away the feature-convert-new toggle.
2. Clear up the unused import assertion.
3. Take away the convertOld operate because it’s not used.

Determine 6: Compose transforms into a brand new rework

You can too extract extra codemods as wanted, combining them in
numerous orders relying on the specified final result.

Determine 7: Put totally different transforms right into a pipepline to type one other rework

The createTransformer Perform

The implementation of the createTransformer operate is comparatively
simple. It acts as a higher-order operate that takes an inventory of
smaller rework capabilities, iterates via the listing to use them to
the foundation AST, and eventually converts the modified AST again into supply
code.

import { API, Assortment, FileInfo, JSCodeshift, Choices } from "jscodeshift";

kind TransformFunction = { (j: JSCodeshift, root: Assortment): void };

const createTransformer =
  (transforms: TransformFunction[]) =>
  (fileInfo: FileInfo, api: API, choices: Choices) => {
    const j = api.jscodeshift;
    const root = j(fileInfo.supply);

    transforms.forEach((rework) => rework(j, root));
    return root.toSource(choices.printOptions || { quote: "single" });
  };

export { createTransformer };

For instance, you would have a rework operate that inlines
expressions assigning the function toggle name to a variable, so in later
transforms you don’t have to fret about these instances anymore:

const shouldEnableNewFeature = featureToggle('feature-convert-new');

if (!shouldEnableNewFeature && someOtherLogic) {
  //...
}

Turns into this:

if (!featureToggle('feature-convert-new') && someOtherLogic) {
  //...
}

Over time, you may construct up a group of reusable, smaller
transforms, which might vastly ease the method of dealing with difficult edge
instances. This strategy proved extremely efficient in our work refining design
system elements. As soon as we transformed one bundle—such because the button
element—we had a couple of reusable transforms outlined, like including feedback
at the beginning of capabilities, eradicating deprecated props, or creating aliases
when a bundle is already imported above.

Every of those smaller transforms might be examined and used independently
or mixed for extra complicated transformations, which accelerates subsequent
conversions considerably. In consequence, our refinement work turned extra
environment friendly, and these generic codemods at the moment are relevant to different inner
and even exterior React codebases.

Since every rework is comparatively standalone, you possibly can fine-tune them
with out affecting different transforms or the extra complicated, composed ones. For
occasion, you may re-implement a rework to enhance efficiency—like
decreasing the variety of node-finding rounds—and with complete check
protection, you are able to do this confidently and safely.