(New Feature) Add EventEmitter to AssemblyScript?

[JairusSW]

Hello everyone,
I was wondering if AssemblyScript planned to support an EventEmitter. I believe it would be a good addition because we could add stream support on top of it. I already have a working example that seems to work seamlessly. Adding an EventEmitter would stray from the Standard Library, but I believe it would be worth it. 😉

Working Example

// EventEmitter Class
export class EventEmitter {
    private maxListeners: number = 10
    private pointers: Map<string, Array<i32>> = new Map<string, Array<i32>>()
    constructor() {}
    emit(event: string, data: string): void {
      if (this.pointers.has(event)) {
        const ptrs = this.pointers.get(event)
        for (let i = 0; i < ptrs.length; i++) {
          call_indirect(ptrs[i], data)
        }
      }
    }
    on(event: string, callback: (data: string) => void): void {
      if (!this.pointers.has(event)) {
        this.pointers.set(event, [load<i32>(changetype<usize>(callback))])
      } else {
        const ptrs = this.pointers.get(event)
        if (ptrs.length > this.maxListeners) {
          throw new Error(`MaxListenersExceededWarning: Possible EventEmitter memory leak detected. ${ptrs.length} ${event} listeners added to [EventEmitter]. Use emitter.setMaxListeners() to increase limit`)
        }
        ptrs.push(load<i32>(changetype<usize>(callback)))
        this.pointers.set(event, ptrs)
      }
    }
    getMaxListeners(): number {
      return this.maxListeners
    }
    setMaxListeners(n: number): void {
      this.maxListeners = n
    }
}

[dcodeIO]

The event emitter pattern typically used around Node.js is a little odd, as it requires quite a bit of dynamicness that is neither type safe nor particularly efficient. I know that @jtenner thought about this quite a lot in context of the (now stale) node lib, and my impression from it was that we'll very likely need either some sort of compiler integration (even though I don't know how that would work yet) or we'll have to resort to a safer (and sadly Node.js-incompatible) pattern.

[JairusSW]

@dcode, Okay! I believe I'll make it into a GitHub module so I can implement

fs.createReadStream(file: string): ReadableStream

in WAKE. :)
I agree, its probably not the best for AS rn.

[JairusSW]

Closing...

[JairusSW]

@dcodeIO , As of dynamicness, It only handles strings at the moment, and for performance, it seems to be ~1.5-2x faster than js when operating <500k times> If it is over 500k - 1m ops, NodeJS is much faster.... Here's a benchmark I performed.

EventEmitter Bench.
NodeJS vs. AssemblyScript

AssemblyScript: v0.18.19
NodeJS: v14.16.0

Bench #1 (1k ops)

• NodeJS: 0.237ms
• AssemblyScript: 0.142ms

Bench #2 (10k ops)

• NodeJS: 2.457ms
• AssemblyScript: 1.477ms

Bench #3 (100k ops)

• NodeJS: 5.362ms
• AssemblyScript: 3.975ms

Bench #4 (250k ops)

• NodeJS: 8.036ms
• AssemblyScript: 8.266ms

Bench #5 (500k ops)

• NodeJS: 11.589ms
• AssemblyScript: 18.931ms

[JairusSW]

Closing (inactive)