source: node_modules/immer/src/core/current.ts

import {
        die,
        isDraft,
        shallowCopy,
        each,
        DRAFT_STATE,
        set,
        ImmerState,
        isDraftable,
        isFrozen
} from "../internal"

/** Takes a snapshot of the current state of a draft and finalizes it (but without freezing). This is a great utility to print the current state during debugging (no Proxies in the way). The output of current can also be safely leaked outside the producer. */
export function current<T>(value: T): T
export function current(value: any): any {
        if (!isDraft(value)) die(10, value)
        return currentImpl(value)
}

function currentImpl(value: any): any {
        if (!isDraftable(value) || isFrozen(value)) return value
        const state: ImmerState | undefined = value[DRAFT_STATE]
        let copy: any
        let strict = true // Default to strict for compatibility
        if (state) {
                if (!state.modified_) return state.base_
                // Optimization: avoid generating new drafts during copying
                state.finalized_ = true
                copy = shallowCopy(value, state.scope_.immer_.useStrictShallowCopy_)
                strict = state.scope_.immer_.shouldUseStrictIteration()
        } else {
                copy = shallowCopy(value, true)
        }
        // recurse
        each(
                copy,
                (key, childValue) => {
                        set(copy, key, currentImpl(childValue))
                },
                strict
        )
        if (state) {
                state.finalized_ = false
        }
        return copy
}