spawn.js

// Syntax proposal:
spawn {
  await somethingAsync()
}

// `spawn` would be available wherever `await` is available
async function fn() {
  await somethingAsync()
  spawn { /* ... */ }
}

// `spawn` enables your code to run concurrently
console.log("logs 1st")
spawn {
  await somethingAsync()
  console.log("logs 3rd")
}
console.log("logs 2nd")

// `spawn` creates its own promise that can be `await`-ed at any time
let promise = spawn { /* ... */ }

// But that promise is also implicitly "await"-ed
let items = []
async function fn() {
  spawn { await sleepMs(200); items.push(1) }
  spawn { await sleepMs(300); items.push(2) }
  spawn { await sleepMs(100); items.push(3) }
}
await fn()
console.log(items) // [3, 1, 2]

// If any spawn's throw an error, it will be immediately thrown in the parent async context
let items = []
async function fn() {
  spawn { await sleepMs(200); items.push(1); throw new Error("wow") }
  spawn { await sleepMs(300); items.push(2) }
  spawn { await sleepMs(100); items.push(3) }
}
try {
  await fn()
} catch (error) {
  console.log(error, items) // "Error: wow", [3, 1]
}

// This would be very useful with `for await` loops to run them concurrently:
for await (const conn of Deno.listen({ port: 4500 })) {
  spawn {
    for await (const { respondWith } of Deno.serveHttp(conn)) {
      respondWith(new Response(body));
    }
  }
}