Build a counter
Build a counter using Durable Objects and Workers.
This example shows how to build a counter using Durable Objects and Workers that can print, increment, and decrement a name
provided by the URL query string parameter, for example, ?name=A
.
index.js// Worker
export default { async fetch(request, env) { let url = new URL(request.url); let name = url.searchParams.get("name"); if (!name) { return new Response( "Select a Durable Object to contact by using" + " the `name` URL query string parameter, for example, ?name=A" ); }
// Every unique ID refers to an individual instance of the Counter class that // has its own state. `idFromName()` always returns the same ID when given the // same string as input (and called on the same class), but never the same // ID for two different strings (or for different classes). let id = env.COUNTER.idFromName(name);
// Construct the stub for the Durable Object using the ID. // A stub is a client Object used to send messages to the Durable Object. let obj = env.COUNTER.get(id);
// Send a request to the Durable Object, then await its response. let resp = await obj.fetch(request.url); let count = await resp.text();
return new Response(`Durable Object '${name}' count: ${count}`); }
};
// Durable Object
export class Counter { constructor(state, env) { this.state = state; }
// Handle HTTP requests from clients. async fetch(request) { // Apply requested action. let url = new URL(request.url);
// Durable Object storage is automatically cached in-memory, so reading the // same key every request is fast. // You could also store the value in a class member if you prefer. let value = (await this.state.storage.get("value")) || 0;
switch (url.pathname) { case "/increment": ++value; break; case "/decrement": --value; break; case "/": // Serves the current value. break; default: return new Response("Not found", { status: 404 }); }
// You do not have to worry about a concurrent request having modified the value in storage. // "input gates" will automatically protect against unwanted concurrency. // Read-modify-write is safe. await this.state.storage.put("value", value);
return new Response(value); }
}
index.tsexport interface Env { COUNTER: DurableObjectNamespace;
}
// Worker
export default { async fetch(request: Request, env: Env) { let url = new URL(request.url); let name = url.searchParams.get("name"); if (!name) { return new Response( "Select a Durable Object to contact by using" + " the `name` URL query string parameter, for example, ?name=A" ); }
// Every unique ID refers to an individual instance of the Counter class that // has its own state. `idFromName()` always returns the same ID when given the // same string as input (and called on the same class), but never the same // ID for two different strings (or for different classes). let id = env.COUNTER.idFromName(name);
// Construct the stub for the Durable Object using the ID. // A stub is a client Object used to send messages to the Durable Object. let obj = env.COUNTER.get(id);
// Send a request to the Durable Object, then await its response. let resp = await obj.fetch(request.url); let count = await resp.text();
return new Response(`Durable Object '${name}' count: ${count}`); }
};
// Durable Object
export class Counter { state: DurableObjectState;
constructor(state: DurableObjectState, env: Env) { this.state = state; }
// Handle HTTP requests from clients. async fetch(request: Request) { // Apply requested action. let url = new URL(request.url);
// Durable Object storage is automatically cached in-memory, so reading the // same key every request is fast. // You could also store the value in a class member if you prefer. let value: number = (await this.state.storage.get("value")) || 0;
switch (url.pathname) { case "/increment": ++value; break; case "/decrement": --value; break; case "/": // Serves the current value. break; default: return new Response("Not found", { status: 404 }); }
// You do not have to worry about a concurrent request having modified the value in storage. // "input gates" will automatically protect against unwanted concurrency. // Read-modify-write is safe. this.state.storage.put("value", value);
return new Response(value.toString()); }
}
Finally, configure your wrangler.toml
file to include a Durable Object binding and migration based on the namespace and class name chosen previously.
wrangler.tomlname = "my-counter"
[[durable_objects.bindings]]
name = "COUNTER"
class_name = "Counter"
[[migrations]]
tag = "v1"
new_classes = ["Counter"]