traverseObject.js

export const DELETE = Symbol('DELETE');

/**
 * Traverse an object and apply a transformation function to each value. 
 * The transformation function is called with the value, the key and the key path.
 * 
 * The transformation function can return a new value or the same value. 
 * If the transformation function returns a new value, the value in the object is replaced with the new value.
 * 
 * The transformation function can return an object.
 * If the transformation function returns an object, the object is traversed as well.
 * 
 * Warning: The transformation could loop infinitely if it always returns an object.
 * 
 * @param obj  { object } - the object to traverse
 * @param transform { (value: unknown, key: string, keyPath: string) => unknown } - a function that transforms the value, the key and the key path
 */
export async function traverse(obj, transform) {
    /**
     * @type { object[] }
     */
    const objectStack = [obj];

    /**
     * @type { string[] }
     */
    const keysStack = []

    while (objectStack.length > 0) {
        const obj = objectStack.pop();
        if (obj) {
            for (const key in obj) {
                keysStack.push(key);
                const keyPath = keysStack.join('.');
                const value = obj[key];
                const transformed = transform(value, key, keyPath);

                if (transformed === DELETE) {
                    delete obj[key];
                    keysStack.pop();
                    continue;
                }

                if (transformed !== value) {
                    obj[key] = transformed;
                }

                if (typeof transformed === 'object' && transformed !== null) {
                    objectStack.push(transformed);
                } else {
                    keysStack.pop();
                }
            }
        }
    }
}

/**
 * Traverse an object and apply a transformation function to each value. 
 * The transformation function is called with the value, the key and the key path.
 * 
 * The transformation function can return a new value or the same value. 
 * If the transformation function returns a new value, the value in the object is replaced with the new value.
 * 
 * The transformation function can return an object.
 * If the transformation function returns an object, the object is traversed as well.
 * 
 * The transformation function can return a promise.
 * If the transformation function returns a promise, the promise is awaited and the resolved value is used.
 * 
 * Warning: The transformation could loop infinitely if it always returns an object.
 * 
 * @param obj { object } - the object to traverse
 * @param transform { (value: unknown, key: string, keyPath: string) => unknown | Promise<unknown> } - a function that transforms the value, the key and the key path
 * @returns
 **/
export async function traverseAsync(obj, transform) {
    /**
     * @type { object[] }
     */
    const objectStack = [obj];

    /**
     * @type { string[] }
     */
    const keysStack = []

    while (objectStack.length > 0) {
        const obj = objectStack.pop();
        if (obj) {
            for (const key in obj) {
                keysStack.push(key);
                const keyPath = keysStack.join('.');
                const value = obj[key];

                const awaitedValue = await value;

                const transformed = await transform(awaitedValue, key, keyPath);

                if (transformed === DELETE) {
                    delete obj[key];
                    keysStack.pop();
                    continue;
                }

                if (value !== transformed) {
                    obj[key] = transformed;
                }

                if (typeof transformed === 'object' && transformed !== null) {
                    objectStack.push(transformed);
                } else {
                    keysStack.pop();
                }
            }
        }
    }
}

const obj = { a: 1, b: { c: [{ a: 2 }, { d: 20 }] } }

traverse(obj, (value, key, keyPath) => {
    if (keyPath === 'a') {
        return DELETE;
    }

    return value
})

obj


const asyncObj = { a: 1, b: { c: Promise.resolve([{ a: 2 }]) } }

traverseAsync(asyncObj, (value, key, keyPath) => {
    if (keyPath === 'a') {
        return DELETE;
    }

    return value
}).then(() => {
    asyncObj
})