Use all toplevel fields if fields not specified

Closes #41

This does not support nested fields. If you have nested fields, the
object associated with the toplevel field will be serialized as JSON
and you will have a JSON string in your CSV.

README.md

@@ -49,7 +49,7 @@ or [use it from the CLI](https://github.com/zemirco/json2csv#command-line-interf
 
 - `options` - **Required**; Options hash.
   - `data` - **Required**; Array of JSON objects.
-  - `fields` - **Required**; Array of Strings, JSON attribute names to use as columns.
+  - `fields` - Array of Strings, JSON attribute names to use as columns. Defaults to toplevel JSON attributes.
   - `fieldNames` Array of Strings, names for the fields at the same indexes.
     Must be the same length as `fields` array.
   - `del` - String, delimiter of columns. Defaults to `,` if not specified.

bin/json2csv.js

@@ -23,10 +23,6 @@ program
   .option('-p, --pretty', 'Use only when printing to console. Logs output in pretty tables.')
   .parse(process.argv);
 
-if(!program.fields && !program.fieldList) {
-  throw new Error('Please specify fields with -f or a list of fields with -l. See json2csv --help');
-}
-
 function getFields(callback) {
   var fields;
 
@@ -41,7 +37,7 @@ function getFields(callback) {
       callback(null, fields);
     });
   } else {
-    fields = program.fields.split(',');
+    fields = program.fields ? program.fields.split(',') : undefined;
     callback(null, fields);
   }
 }

lib/json2csv.js

@@ -45,12 +45,16 @@ module.exports = function (params, callback) {
 function checkParams(params, callback) {
   // if data is an Object, not in array [{}], then just create 1 item array.
   // So from now all data in array of object format.
-  if (!(params.data instanceof Array)) {
+  if (!Array.isArray(params.data)) {
     var ar = [];
     ar[0] = params.data;
     params.data = ar;
   }
 
+  if (!params.fields && params.data && params.data.length) {
+    params.fields = Object.keys(params.data[0]);
+  }
+
   //#check fieldNames
   if (params.fieldNames && params.fieldNames.length !== params.fields.length) {
     callback(new Error('fieldNames and fields should be of the same length, if fieldNames is provided.'));