Extracting records of type "withdraw_rewards" from a multi-level data structure

Question

Re-posting from StackOverflow as this is a place to review code that is already working.

I would like to know if there is a better way to deal with nested forEach when it comes to dealing with objects with properties that are nested arrays themselves.

My object (summarized):

{
 ...,
 "tx_responses": [
   {
     ...
     "logs" : [
       {
         ...,
         "events": [
             {
                 "type": "coin_received",
                 "attributes": [
                     {
                         "key": "receiver",
                         "value": "somesome"
                     },
                     {
                         "key": "amount",
                         "value": "somesome"
                     }
                 ]
             },
             ...
             {
                 "type": "transfer",
                 "attributes": [
                     {
                         "key": "recipient",
                         "value": "somesome"
                     },
                     {
                         "key": "sender",
                         "value": "somesome"
                     },
                     {
                         "key": "amount",
                         "value": "somesome"
                     }
                 ]
             },
             {
                 "type": "withdraw_rewards",
                 "attributes": [
                     {
                         "key": "amount",
                         "value": "somesomesomehere"
                     },
                     {
                         "key": "validator",
                         "value": "somesome"
                     }
                 ]
             },
             ...
         ]
     }
 ],
...

I am essentially trying to extract all { key: 'amount', value: 'somesomesomehere' } objects in the attributes array of the "type" : "withdraw_rewards" object in the events array.

Currently this is the code I wrote to carry out my task:

getWithdrawnAmounts: async(del_addr_) => {
    let withdrawnAmounts = [];
    const res = await axios.get("some_url_that_uses_del_addr_");
    res.data.tx_responses.forEach(txr => {
        txr.logs.forEach(log => {
            log.events.forEach(evnt => {
                if (evnt.type == "withdraw_rewards") {
                    evnt.attributes.forEach(attr => {
                        if (attr.key == "amount") {
                            withdrawnAmounts.push(attr);
                        }
                    })
                }
            })
        })
    });
    return withdrawnAmounts;
}

The code helps me to get what I need, but I was wondering if there is a better way to write my code so that I dont have to use so many nested .forEach methods. I was wondering if I should use .flat() or .flatMap() but I'm curious to know how would people approach this?

Answer 1

The pipeline can be written simpler:

• replacing nested .forEach using .flatMap
• replacing conditionals inside .forEach using .filter

Also, instead of appending to withdrawnAmounts in the deepest .forEach, you can make the pipeline return a filtered list.

return res.data.tx_responses
  .flatMap(txr => txr.logs)
  .flatMap(log => log.events)
  .filter(evnt => evnt.type === "withdraw_rewards")
  .flatMap(evnt => evnt.attributes)
  .filter(attr => attr.key === "amount");

Answer 2

here is example if you want to use flatmap.

It's an improvement of original as i am using only 3 flatmaps and forEach loop.

        const logs = data.tx_responses.flatMap(item=>item.logs);
            const events = logs.flatMap(item=>item.events)
            const attributes = events.flatMap(item=> { 
            if(item.type == "withdraw_rewards") {
return item.attributes
}
            else{
 return null
}
            })
attributes.forEach(attr => {
                    if (attr.key == "amount") {
                        withdrawnAmounts.push(attr);
                    }
                })