Explanation

Many projects choose to extract common shared logic into small helper functions. TypeScript projects often use small user-defined type guards to inform type narrowing. Unfortunately, the overhead of extracting logic into functions can hurt application performance before JIT optimizers fully kick in.[^1]

This TypeScript transformation plugin detects calls to small one-line functions and inlines them in the output JavaScript. The resultant code will function the same regardless of the transformation.

Example

Given the following function:

export function isNotFalsy(value: unknown) {
	return !!value;
}

Before:

export const value = isNotFalsy("Hello!");

After:

export const value = !!"Hello!";

Note: this transformer does not remove the original function declarations. Use a separate tool after the transform, such as Terser, if you'd like to configure that.

Usage

npm i ts-function-inliner

Per github.com/Microsoft/TypeScript/issues/14419, TSConfig plugins don't support transformers. However, you can use this in other pipelines.

Usage with Gulp

Specify it as a custom transformer with gulp-typescript:

import gulp from "gulp";
import ts from "gulp-typescript";
import { transformerProgram } from "ts-function-inliner";

gulp.task("typescript", function () {
	gulp
		.src("src/**/*.ts")
		.pipe(
			ts({
				getCustomTransformers: (program) => ({
					before: [transformerProgram(program)],
				}),
			}),
		)
		.pipe(gulp.dest("lib"));
});

Development

See .github/CONTRIBUTING.md, then .github/DEVELOPMENT.md. Thanks! ⚡

Contributors

💝 This package was templated with create-typescript-app using the Bingo engine.

[^1]: See Microsoft/TypeScript: Added some Type type predicates internally #50010, which caused a 1-2% performance hit in TypeScript.