feat(json2csv): use sort function for sortHeader option (#217)

Author: mebibou

README.md

@@ -96,7 +96,7 @@ Looking for examples? Check out the Wiki: [json-2-csv Wiki](https://github.com/m
     * Note: Using this option may override other options, including `useDateIso8601Format` and `useLocaleFormat`.
   * `prependHeader` - Boolean - Should the auto-generated header be prepended as the first line in the CSV?
     * Default: `true`
-  * `sortHeader` - Boolean - Should the header keys be sorted in alphabetical order? 
+  * `sortHeader` - Boolean or Function - Should the header keys be sorted in alphabetical order? or pass a function to use a custom sorting function
     * Default: `false`
   * `trimFieldValues` - Boolean - Should the field values be trimmed?
     * Default: `false`

lib/converter.d.ts

@@ -85,7 +85,7 @@ export interface IFullOptions extends ISharedOptions {
    * Should the header keys be sorted in alphabetical order
    * @default false
    */
-  sortHeader?: boolean;
+  sortHeader?: boolean|((a: any, b: any) => number);
 
   /**
    * Should array values be "unwound" such that there is one line per value in the array?

lib/json2csv.js

@@ -103,7 +103,7 @@ const Json2Csv = function(options) {
      */
     function sortHeaderFields(fieldNames) {
         if (options.sortHeader) {
-            return fieldNames.sort();
+            return typeof options.sortHeader === 'function' ? fieldNames.sort(options.sortHeader) : fieldNames.sort();
         }
         return fieldNames;
     }

test/config/testCsvFilesList.js

@@ -27,6 +27,7 @@ const fs = require('fs'),
         {key: 'extraLine', file: '../data/csv/extraLine.csv'},
         {key: 'noHeader', file: '../data/csv/noHeader.csv'},
         {key: 'sortedHeader', file: '../data/csv/sortedHeader.csv'},
+        {key: 'sortedHeaderCustom', file: '../data/csv/sortedHeaderCustom.csv'},
         {key: 'emptyFieldValues', file: '../data/csv/emptyFieldValues.csv'},
         {key: 'quotedEmptyFieldValue', file: '../data/csv/quotedEmptyFieldValue.csv'},
         {key: 'csvEmptyLastValue', file: '../data/csv/csvEmptyLastValue.csv'},

test/data/csv/sortedHeaderCustom.csv

@@ -0,0 +1,3 @@
+optionalField,object.subField,number,isBoolean,arrayOfStrings
+this one has it,subValue,5,true,"[""test1"",""test2""]"
+null,subValue,7,false,"[""test3"",""test4""]"

test/json2csv.js

@@ -328,6 +328,16 @@ function runTests(jsonTestData, csvTestData) {
                 });
             });
 
+            it('should sort the header with a custom function in the csv', (done) => {
+                converter.json2csv(jsonTestData.assortedValues, (err, csv) => {
+                    if (err) done(err);
+                    csv.should.equal(csvTestData.sortedHeaderCustom);
+                    done();
+                }, {
+                    sortHeader: (a, b) => b.localeCompare(a)
+                });
+            });
+
             it('should trim the header fields when specified', (done) => {
                 converter.json2csv(jsonTestData.trimHeader, (err, csv) => {
                     if (err) done(err);