ESUpgrade

esupgrade

Keeping your JavaScript and TypeScript code up to date with full browser compatibility.

Sponsors

Usage

esupgrade is safe and meant to be used automatically on your codebase. We recommend integrating it into your development workflow using [pre-commit], [husky], or as an agent skill.

CLI

To try it out on a repository without writing changes, run:

npx -y esupgrade $(git ls-files | grep -E -i -w '.*\.(t|j)sx?')

To transform code from standard input, pass - as the input path:

echo 'var x = 1;' | npx esupgrade -

For help with available options:

npx esupgrade --help

pre-commit

uvx pre-commit install

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/codingjoe/esupgrade
    rev: 2025.0.2 # Use the latest version
    hooks:
      - id: esupgrade

pre-commit run esupgrade --all-files

Husky

Assuming Husky is already initialized and .husky/pre-commit already contains set -e, append:

echo "git diff --cached --name-only --diff-filter=ACMR -z -- '*.js' '*.jsx' '*.ts' '*.tsx' '*.mjs' '*.cjs' | xargs -0 sh -c 'test \"\$#\" -eq 0 && exit 0; npx -y esupgrade -- \"\$@\"' sh" >> .husky/pre-commit
echo "git diff --cached --name-only --diff-filter=ACMR -z -- '*.js' '*.jsx' '*.ts' '*.tsx' '*.mjs' '*.cjs' | xargs -0 sh -c 'test \"\$#\" -eq 0 && exit 0; git add -- \"\$@\"' sh" >> .husky/pre-commit

Agent Skill

esupgrade is available as a skill in [Claude Code]. To use it:

1. Run /plugin marketplace add codingjoe/esupgrade
2. Run /plugin install esupgrade@esupgrade

The skill will analyze your selected code and suggest transformations based on the Baseline browser support policy.

Browser Support & Baseline

All transformations are based on [Web Platform Baseline][baseline] features. Baseline tracks which web platform features are safe to use across browsers.

By default, esupgrade uses widely available features, meaning they work in all major browsers (Chrome, Edge, Safari, Firefox) for at least 30 months. This ensures full compatibility while keeping your code modern.

You can opt into newly available features (available in all browsers for 0-30 months) with:

npx esupgrade --baseline newly-available <files>

For more information about Baseline browser support, visit [web.dev/baseline][baseline].

Supported File Types & Languages

• .js - JavaScript
• .jsx - React/JSX
• .ts - TypeScript
• .tsx - TypeScript with JSX
• .mjs - ES Modules
• .cjs - CommonJS

Transformations

Widely available

var → [const][mdn-const] & [let][mdn-let]

-var x = 1;
-var y = 2;
-y = 3;
+const x = 1;
+let y = 2;
+y = 3;

String concatenation → [Template literals][mdn-template-literals]

-const greeting = 'Hello ' + name + '!';
-const message = 'You have ' + count + ' items';
+const greeting = `Hello ${name}!`;
+const message = `You have ${count} items`;

Special handling for escape sequences and formatting:

• Escape sequences: \r (carriage return) is preserved, while \n (newline) is converted to actual newlines

  -const text = "Line 1\n" + "Line 2";
  +const text = `Line 1
  +Line 2`;