es-checker

ES-Checker is a tool that tells you which modern JavaScript features your code environment actually supports. Instead of guessing whether your browser or Node.js version can handle a particular piece of syntax, you can ask the library directly and get a yes-or-no answer.

The library works by running small test snippets for each JavaScript feature. When you ask "does this environment support arrow functions?" or "can I use the spread operator?", ES-Checker runs a quick internal check and returns true or false. You can then write conditional code that uses the modern syntax if it's available, or falls back to an older alternative if it's not. It covers a wide range of features introduced in recent JavaScript standards—things like let and const declarations, template strings, classes, promises, generators, and many others.

You can use ES-Checker in three different ways. If you're building a command-line tool, you can install it globally and run it as a terminal command to see a full report of what your Node.js environment supports. If you're writing Node.js code, you can include it as a package and check specific features in your scripts before using them. Or if you're writing for the browser, you can include a single script file and use the same feature-detection API in your HTML and JavaScript.

The main value here is avoiding runtime errors and compatibility headaches. Instead of writing code that breaks in older environments or hoping your tooling properly transpiles everything, you can write code that gracefully adapts to what's available. This is especially useful if you're maintaining libraries or applications that need to run across a range of user environments, or if you're working in Node.js and need to know exactly which version's features you can count on.