Convert DynamoDB Export to standard JSON

dynamo-to-json.js

let file = './data.dynamodata';

function mapper(data) {
	const val =        obj => Object.keys(obj).reduce((o,k) => o[k],obj);
	const defaultFn =  (obj, key) => ({[key]: val(obj)});
	const recurFn =    (obj, key) => ({[key]: mapper(val(obj))});
	const valType = {
		"NULL":  (obj, key) => ({[key]:null}),
		"BOOL":  defaultFn,
		"SS":    defaultFn, 
		"BB":    defaultFn, 
		"NS":    defaultFn, 
		"BS":    defaultFn, 
		"S":     defaultFn, 
		"L":     recurFn,
		"M":     recurFn,
		"N":     (obj, key) => ({[key]: parseFloat(obj["N"])}),
	}
	let isArray = Array.isArray(data);
	let result = (isArray ? data : [data]).map(dynamoRow => {
		return (isArray ?
			(() => {
					let type = Object.keys(dynamoRow)[0];
					let convert = valType[type];
					return convert(dynamoRow, "key")["key"];
				})() :
			Object.keys(dynamoRow)
				.reduce((obj, key) => {
					let type = Object.keys(dynamoRow[key])[0];
					let convert = valType[type];
					return Object.assign(obj, convert(dynamoRow[key], key))
				}, {}));
	});
	return (isArray ? result : result[0]);
}

var ws = require('fs').createWriteStream(file+".json", {encoding: 'utf8'});
ws.isTTY = true;
ws.write('[\n');
var lineReader = require('readline').createInterface({
  input: require('fs').createReadStream(file)
});

lineReader.on('line', (line) => {
	ws.write(JSON.stringify(mapper(JSON.parse(line))) + ',\n');
})
lineReader.on('close', () => { ws.write(']'); })