Method concat

packages/mobx/src/types/legacyobservablearray.ts:81–88

(...arrays: T[][])

    }

    concat(...arrays: T[][]): T[] {
        ;(this[$mobx] as ObservableArrayAdministration).atom_.reportObserved()
        return Array.prototype.concat.apply(
            (this as any).slice(),
            //@ts-ignore
            arrays.map(a => (isObservableArray(a) ? a.slice() : a))
        )
    }

    get length(): number {
        return (this[$mobx] as ObservableArrayAdministration).getArrayLength_()