update doc

README.md

@@ -5,8 +5,9 @@
 import DdbCsv from 'dynamocsv';
 const service = new DdbCsv({
   client: new DynamoDBClient({}),
-  target: 'dump.csv',
+  target: 'dump.csv',  // (string, WritableStream, async callback)
   input: { tableName: 'ddb_test_table', index: 'awesomeness' },
+  format: 'csv', // (csv | json | object)
   query: {
     keyCondExpressionMap: {
       hash: 'test',
@@ -26,12 +27,13 @@ await service.exec();
 
 ### Args
 + *client* - An instance of DynamoDBClient, example uses aws-sdk 3, but v2 should also work
-+ *target* - file name with extension, or an instance of Node.js WriteStream.
++ *target* - file name with extension, or an instance of Node.js WriteStream or async callback. ie. `async (rows) => { const result = await writeToDb(rows); return result.count; }`;
++ *format* - csv (default) | json | object - object requires a writable stream in object mode or use an async callback to capture values.k
 + *input*
     + *tableName* - string (required)
     + *index* - string (optional)
     + *limit* - number (optional, default 2000)
 + *query* - a simplified mapping to generate `KeyConditionExpression` and `FilterExpression`. See example above - key/val pair generates a simple equality condition, use an object to specify operator and value if needed.
     + *keyCondExpressionMap*
     + *filterExpressionMap*
-+ *rowPredicate* - (row, context) => row - a function that is called for each row. See example above - use the `context` methods to modify headers as needed.
++ *rowPredicate* - `(row, context) => row` - a function that is called for each row. See example above - use the `context` methods to modify headers as needed.

dynamocsv.ts

@@ -93,7 +93,7 @@ export default class Dynamocsv {
     return this.headers;
   }
 
-  applyRowPredicate = (row: any) => {
+  private applyRowPredicate = (row: any) => {
     return this.rowPredicate ? this.rowPredicate(row, this) : row;
   };