variables-secrets.md

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🔑 Variables and Secrets

Bindings

Variable and secrets are bound as follows:

const mf = new Miniflare({
  bindings: {
    KEY1: "value1",
    KEY2: "value2",
  },
});

.env Files

Variables and secrets are automatically loaded from a .env file in the current directory. This is especially useful for secrets if your .env file is .gitignored. .env files look something like this:

KEY1=value1
# Woah, comments!
KEY2=value2

You can also specify the path to a custom .env file:

const mf = new Miniflare({
  envPath: ".env.test",
});

Text and Data Blobs

Text and data blobs can be loaded from files. File contents will be read and bound as strings and ArrayBuffers respectively.

const mf = new Miniflare({
  textBlobBindings: { TEXT: "text.txt" },
  dataBlobBindings: { DATA: "data.bin" },
});

Bindings Priority

Higher priority bindings override lower priority bindings with the same name. The order (from lowest to highest priority) is:

1. Variables from wrangler.toml [vars]
2. Variables from .env files
3. WASM module bindings (--wasm, [wasm_modules])
4. Text blob bindings (--text-blob, [text_blobs])
5. Data blob bindings (--data-blob, [data_blobs])
6. Custom bindings (--binding, bindings)

Globals

Injecting arbitrary globals is not supported by workerd. If you're using a service worker, bindings will be injected as globals, but these must be JSON-serialisable.

Miniflare will always set the global variable MINIFLARE to true in its sandbox. You can use this as an escape hatch to customise behaviour during local development:

if (globalThis.MINIFLARE) {
  // Do something when running in Miniflare
} else {
  // Do something else when running in the real Workers environment
}