mobx/src/api/become-observed.ts

Simple, scalable state management.

import {
    IComputedValue,
    IObservable,
    IObservableArray,
    Lambda,
    ObservableMap,
    getAtom,
    ObservableSet,
    isFunction,
    IObservableValue
} from "../internal"

const ON_BECOME_OBSERVED = "onBO"
const ON_BECOME_UNOBSERVED = "onBUO"

export function onBecomeObserved(
    value:
        | IObservable
        | IComputedValue<any>
        | IObservableArray<any>
        | ObservableMap<any, any>
        | ObservableSet<any>
        | IObservableValue<any>,
    listener: Lambda
): Lambda
export function onBecomeObserved<K, V = any>(
    value: ObservableMap<K, V> | Object,
    property: K,
    listener: Lambda
): Lambda
export function onBecomeObserved(thing, arg2, arg3?): Lambda {
    return interceptHook(ON_BECOME_OBSERVED, thing, arg2, arg3)
}

export function onBecomeUnobserved(
    value:
        | IObservable
        | IComputedValue<any>
        | IObservableArray<any>
        | ObservableMap<any, any>
        | ObservableSet<any>
        | IObservableValue<any>,
    listener: Lambda
): Lambda
export function onBecomeUnobserved<K, V = any>(
    value: ObservableMap<K, V> | Object,
    property: K,
    listener: Lambda
): Lambda
export function onBecomeUnobserved(thing, arg2, arg3?): Lambda {
    return interceptHook(ON_BECOME_UNOBSERVED, thing, arg2, arg3)
}

function interceptHook(hook: "onBO" | "onBUO", thing, arg2, arg3) {
    const atom: IObservable =
        typeof arg3 === "function" ? getAtom(thing, arg2) : (getAtom(thing) as any)
    const cb = isFunction(arg3) ? arg3 : arg2
    const listenersKey = `${hook}L` as "onBOL" | "onBUOL"

    if (atom[listenersKey]) {
        atom[listenersKey]!.add(cb)
    } else {
        atom[listenersKey] = new Set<Lambda>([cb])
    }

    return function () {
        const hookListeners = atom[listenersKey]
        if (hookListeners) {
            hookListeners.delete(cb)
            if (hookListeners.size === 0) {
                delete atom[listenersKey]
            }
        }
    }
}