Detecting if we are running in dev mode or in production mode in CloudFlare Worker - cloudflare

Question

I need to know in my worker script if it is running using wrangler dev locally
or it is running at cloudflare after wrangelr publish.
Is there an environment variable that tells me that, or a request headers?
Code snippet would be highly appriciated.
Thank you.

Answer 1

There isn't a builtin variable, but you can populate such info yourself by defining environments in your wrangler.toml
For example, if we say the topmost [vars] are meant to be used in production, we can declare another variable set meant to be used in local environment. (the environment name is irrelevant)
type = "webpack"
webpack_config = "webpack.config.js"
# these will be used in production
vars = { WORKER_ENV = "production", SENTRY_ENABLED = true }
[env.local]
# these will be used only when --env=local
vars = { WORKER_ENV = "local", SENTRY_ENABLED = false }
From then on, if you run your worker locally using
wrangler dev --env=local
the value of binding WORKER_ENV will be populated as defined under [env.local.vars].
By the way, the syntax of wrangler.toml above is equivalent to
type = "webpack"
webpack_config = "webpack.config.js"
[vars]
WORKER_ENV = "production"
SENTRY_ENABLED = true
[env]
[env.local]
[env.local.vars]
WORKER_ENV = "local"
SENTRY_ENABLED = false
Which I believe it's easier to understand

Answer 2

I believe there is an official update for this now (as of November 2022):
When developing locally, you can create a .dev.vars file in the
project root which allows you to define variables that will be used
when running wrangler dev or wrangler pages dev, as opposed to using
another environment and [vars] in wrangler.toml.
Cloudflare Workers documentation