Dynamically pass keys to map to new object

Question

Sorry for the confusing title, wasn't sure how to describe this in a one liner.

I have the following utility function:

module.exports.reduceObject = item => (({ price, suggested_price }) => ({ price, suggested_price }))(item);

Which takes the values from the keys price and suggest_price and returns a new object with just those keys and values.

I can then turn an object like this:

inspect_link: 'steam://rungame/730/76561202255233023/+csgo_econ_action_preview%20S76561198279893060A%item_id%D9567622191659726240',
price: '2.15',
suggested_price: '2.90',
is_featured: false,
float_value: '-1.00000',
pattern_info: 
 { paintindex: 0,
   paintseed: null,
   rarity: 3,
   quality: 4,
   paintwear: null },
is_mine: false,
tags: { type: 'Collectible', quality: 'Normal', rarity: 'High Grade' },
fraud_warnings: [],
stickers: null,
updated_at: 1501880427 }

Into it's reduced version:

{"price":"2.59","suggested_price":"1.41"}

Which I'm then storing in a MongoDB database.

I'd like to be able to pass in the keys (such as price , suggested_price dynamically so I can reduce any object to a smaller version of itself, but I'm struggling to find a good implementation.

I wrote something such as:

module.exports.reduceObject = (item, keys) => (({ ...keys }) => ({ ...keys }))(item);

which isn't valid, but I honestly have no idea how to even approach this.

Can anybody offer a solution?

Answer 1

There is already a powerful lodash library which does what you need. It has pick function which returns an object composed of the picked object properties:

let newItem = _.pick(item, ['price', 'suggested_price']);

Answer 2

I find lodash's implementation hard to read. If you're like me, here's a simpler implementation:

function pick(object, keys) {
    const result = {};
    for (const key of keys) {
        if (object.hasOwnProperty(key)) {
            result[key] = object[key];
        }
    }
    return result;
}

Depending on your use, it can be important to check whether the key is actually in the source object. This has slipped me up before.