Do ES6 features get transpiled into ES5 when utilized in TypeScript?

After implementing ES6 features such as template strings, arrow functions, and destructuring in a TypeScript file, I compile the code to regular JavaScript...

Does the TypeScript compiler also compile the ES6 syntax, or do I need to utilize another compiler like Babel?

Answer №1

Does the TypeScript compiler also handle ES6 syntax, or do I need Babel for that?

I have a different perspective on Fylax's response. The TypeScript compiler is capable of converting ES6 syntax to ES3 or ES5 without requiring an additional tool like Babel.

TypeScript transpiles new features such as `let`, `for ... of` loops, arrow functions, rest parameters, etc., into ES3 or ES5. However, it does not include polyfills by default. To use modern APIs like `Promise` on older ES3 or ES5 virtual machines, you need to:

  1. Integrate a polyfill (e.g., [es6-promise](https://github.com/stefanpenner/es6-promise)) to make the API accessible;
  2. Instruct the compiler to utilize standard typings for this API.

This approach offers flexibility and control. With TypeScript, you can carefully select necessary polyfills and test them across various target browsers.

By default, when targeting ES3 or ES5, the compiler does not incorporate definitions for recent ECMAScript APIs. Refer to [the documentation](http://www.typescriptlang.org/docs/handbook/compiler-options.html) for more details:

Note: If `--lib` is unspecified, a default library is injected. The default libraries are:

► For `--target ES5`: `dom, es5, scripthost`

If a polyfill exposes an API, we can configure the compiler to leverage it. Below is an example `tsconfig.json` configuration for using promises in an ES5 VM:

{
  "compilerOptions": {
    "target": "es5",
    "lib": ["dom", "es5", "es2015.promise"]
  }
}

Nevertheless, Babel has slightly broader support for converting features to ES5 compared to TypeScript. Refer to [Kangax's compatibility table](http://kangax.github.io/compat-table/es6/) for further insights.

Answer №2

To convert your code from ES6 to ES5, consider using additional compilers.

Using TypeScript can automate much of this process for you by translating features like let to var and arrow functions to standard functions with the proper scope and bindings.

Note: In most cases, providing TypeScript with a polyfill library should suffice, eliminating the need for external compilers.

Only in rare instances where neither a transpiler nor polyfill covers your specific needs will you require an extra compiler.

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