Sample filter / map / reduce (XRP Transaction Sum)

/* Filter / Map / Reduce on arrays: Imagine a funnel `filter`, `map`, `reduce`: They take an array as input and at the other send the input is returned processed. filter = decide what should be in the output array map = modify the content of each object that will be in the output array reduce = aggregate the input to some output */ const RippleAPI = require('ripple-lib').RippleAPI const api = new RippleAPI({ server: 'wss://rippled.xrptipbot.com' }) api.connect().then(() => { return api.getTransactions('rPdvC6ccq8hCdPKSPJkPmyZ4Mi1oG2FFkT', { minLedgerVersion: 36542093 }).then(transactions => { // `transactions` is an array with transaction objects. let sum = transactions .filter(tx => { // The .filter runs for each tx in transactions, we call each // transaction (each array member) 'tx'. Only return true // (so: array object to next part of the chain) if this is valid return tx.type === 'payment' && tx.outcome.result === 'tesSUCCESS' && tx.outcome.deliveredAmount.currency === 'XRP' }) .map(tx => { // Convert to drops, prevent rounding errors let value = parseFloat(tx.outcome.deliveredAmount.value) * 1000000 return Math.round(value) }) .reduce((existingTotal, thisValue) => { return existingTotal + thisValue }, 0) // 0 = 2nd argument = startValue console.log('Sum in XRP:', sum / 1000000) }) }).then(() => { }).catch(console.error)