custom transformers

[j-ibarra]

config

{
	name: "@hey-api/transformers",
	dates: true,
	bigInt: false,
	transformers: [decimalExpressions],
}

custom transformer

import { compiler, type expressionTransformer } from "@hey-api/openapi-ts";

export const decimalExpressions: expressionTransformer = ({
	dataExpression,
	schema,
	file,
}) => {
	if (schema.type !== "string" || schema.format !== "decimal") {
		return undefined;
	}

	const decimalCallExpression =
		dataExpression !== undefined
			? compiler.newExpression({
					argumentsArray: [
						typeof dataExpression === "string"
							? compiler.identifier({ text: dataExpression })
							: dataExpression,
					],
					expression: compiler.identifier({ text: "Decimal" }),
				})
			: undefined;

	if (decimalCallExpression) {
		if (typeof dataExpression === "string") {
			return [decimalCallExpression];
		}

		file.import({
			module: "decimal.js",
			name: "Decimal",
		});

		if (dataExpression) {
			return [
				compiler.assignment({
					left: dataExpression,
					right: decimalCallExpression,
				}),
			];
		}
	}

	return [];
};

output

import { Decimal } from "decimal.js";
import type { myResponse } from "./types.gen";

const myResponseSchemaResponseTransformer = (data: any) => {
	if (data.amount) {
		data.amount = new Decimal(data.amount);
	}
	if (data.createdAt) {
		data.createdAt = new Date(data.createdAt);
	}
	return data;
};

export const myResponseTransformer = async (
	data: any,
): Promise<myResponse> => {
	data = myResponseSchemaResponseTransformer(data);
	return data;
};

Limitation

In types.gen.ts you need to change the string type to the correct type (in this example Decimal) as the Date type

export type myResponse = {
	/**
	 * The amount to withdraw
	 */
	amount?: string;
	/**
	 * The time the preview was created
	 */
	createdAt?: Date;
};

[bolt-new-by-stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[changeset-bot]

🦋 Changeset detected

Latest commit: 565830b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@hey-api/openapi-ts	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
hey-api-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 7, 2025 1:17am

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/hey-api/openapi-ts/@hey-api/nuxt@2281

npm i https://pkg.pr.new/hey-api/openapi-ts/@hey-api/openapi-ts@2281

npm i https://pkg.pr.new/hey-api/openapi-ts/@hey-api/vite-plugin@2281

commit: 565830b

[codecov]

Codecov Report

Attention: Patch coverage is 6.31579% with 89 lines in your changes missing coverage. Please review.

Project coverage is 24.01%. Comparing base (9cf1a08) to head (565830b).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
.../@hey-api/transformers/expressions-transformers.ts	4.34%	66 Missing ⚠️
...api-ts/src/plugins/@hey-api/transformers/plugin.ts	4.16%	23 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2281      +/-   ##
==========================================
- Coverage   24.02%   24.01%   -0.01%     
==========================================
  Files         313      314       +1     
  Lines       28927    28949      +22     
  Branches     1227     1227              
==========================================
+ Hits         6949     6953       +4     
- Misses      21969    21987      +18     
  Partials        9        9              

Flag	Coverage Δ
unittests	24.01% <6.31%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.