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JavaScript and web standards

The Workers runtime provides the following standardized APIs for use by scripts running at the edge.

JavaScript standards

Cloudflare Workers uses the V8 JavaScript engine from Google Chrome. The Workers runtime is updated at least once a week, to at least the version that is currently used by Chrome's stable release. This means you can safely use the latest JavaScript features, with no need for transpilers.

All of the standard built-in objects supported by the current Google Chrome stable release are supported, with a few notable exceptions:

  • eval() is not allowed for security reasons.
  • new Function is not allowed for security reasons.
  • returns the time of the last I/O; it does not advance during code execution.

Web global APIs

The following methods are available per the Worker Global Scope:

Base64 utility methods


EventTarget and Event

The EventTarget and Event API allow objects to publish and subscribe to events.

AbortController and AbortSignal

The AbortController and AbortSignal APIs provide a common model for canceling asynchronous operations.

Fetch global

Encoding API

Both TextEncoder and TextDecoder support UTF-8 encoding/decoding.

Go to the docs


The URL API supports urls conforming to http and https schemes.

Go to the docs