@snap/camera-kit/dist/events/scan.js

Camera Kit Web

import { TypedCustomEvent } from "./TypedCustomEvent";
import { TypedEventTarget } from "./TypedEventTarget";
export const scan = (seedState) => (source, eventTypes, accumulator) => {
    let state = seedState;
    const sink = new TypedEventTarget();
    const listener = (event) => {
        state = accumulator(state, event);
        sink.dispatchEvent(new TypedCustomEvent("state", state));
    };
    let hasListener = false;
    sink.addEventListener = new Proxy(sink.addEventListener, {
        apply: (target, thisArg, args) => {
            if (hasListener)
                throw new Error("Cannot add another event listener. The TypedEventTarget returned by scan only " +
                    "supports a single listener, and one has already been added.");
            hasListener = true;
            eventTypes.forEach((eventType) => source.addEventListener(eventType, listener));
            target.apply(thisArg, args);
        },
    });
    sink.removeEventListener = new Proxy(sink.removeEventListener, {
        apply: (target, thisArg, args) => {
            eventTypes.forEach((eventType) => source.removeEventListener(eventType, listener));
            target.apply(thisArg, args);
        },
    });
    return sink;
};
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