Convert lib to synchronous operation. (#126)

* Convert lib to synchronous operation. Optional callback is still functional but uses process.nextTick() to avoid accidentally-synchronous operation. Previous versions had an async API but actually operated synchronously. * Update README and bin for synchronous operation. * Update typescript definition for synchronous operation.
zemirco · Jul 7, 2016 · b91158b · b91158b
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diff --git a/README.md b/README.md
@@ -23,10 +23,13 @@ Include the module and run or [use it from the Command Line](https://github.com/
 var json2csv = require('json2csv');
 var fields = ['field1', 'field2', 'field3'];
 
-json2csv({ data: myData, fields: fields }, function(err, csv) {
-  if (err) console.log(err);
-  console.log(csv);
-});
+try {
+  console.log(json2csv({ data: myData, fields: fields }));
+} catch (err) {
+  // Errors are thrown for bad options, or if the data is empty and no fields are provided.
+  // Be sure to provide fields if it is possible that your data array will be empty.
+  console.error(err);
+}
 ```
 
 ## Features
@@ -62,7 +65,7 @@ json2csv({ data: myData, fields: fields }, function(err, csv) {
   - `flatten` - Boolean, flattens nested JSON using [flat]. Defaults to `false`.
   - `excelStrings` - Boolean, converts string data into normalized Excel style data.
   - `includeEmptyRows` - Boolean, includes empty rows. Defaults to `false`.
-- `callback` - **Required**; `function (error, csvString) {}`. To create a promise, you can use `var toCSV = Bluebird.promisify(json2csv)`, see [Bluebird] docs.
+- `callback` - `function (error, csvString) {}`. If provided, will callback asynchronously. Only supported for compatibility reasons.
 
 #### Example `fields` option
 ``` javascript
@@ -113,12 +116,10 @@ var myCars = [
   }
 ];
 
-json2csv({ data: myCars, fields: fields }, function(err, csv) {
-  if (err) console.log(err);
-  fs.writeFile('file.csv', csv, function(err) {
-    if (err) throw err;
-    console.log('file saved');
-  });
+var csv = json2csv({ data: myCars, fields: fields });
+fs.writeFile('file.csv', csv, function(err) {
+  if (err) throw err;
+  console.log('file saved');
 });
 ```
 
@@ -162,10 +163,8 @@ Use a custom delimiter to create tsv files. Add it as the value of the del prope
 var json2csv = require('json2csv');
 var fields = ['car', 'price', 'color'];
 
-json2csv({ data: myCars, fields: fields, del: '\t' }, function(err, tsv) {
-  if (err) console.log(err);
-  console.log(tsv);
-});
+var tsv = json2csv({ data: myCars, fields: fields, del: '\t' });
+console.log(tsv);
 ```
 
 Will output:
@@ -189,10 +188,8 @@ var json2csv = require('json2csv');
 var fields = ['car', 'price'];
 var fieldNames = ['Car Name', 'Price USD'];
 
-json2csv({ data: myCars, fields: fields, fieldNames: fieldNames }, function(err, csv) {
-  if (err) console.log(err);
-  console.log(csv);
-});
+var csv = json2csv({ data: myCars, fields: fields, fieldNames: fieldNames });
+console.log(csv);
 ```
 
 ### Example 5
@@ -210,10 +207,8 @@ var opts = {
   quotes: ''
 };
 
-json2csv(opts, function(err, csv) {
-  if (err) console.log(err);
-  console.log(csv);
-});
+var csv = json2csv(opts);
+console.log(csv);
 ```
 
 Results in
@@ -249,12 +244,10 @@ var myCars = [
   }
 ];
 
-json2csv({ data: myCars, fields: fields }, function(err, csv) {
-  if (err) console.log(err);
-  fs.writeFile('file.csv', csv, function(err) {
-    if (err) throw err;
-    console.log('file saved');
-  });
+var csv = json2csv({ data: myCars, fields: fields });
+fs.writeFile('file.csv', csv, function(err) {
+  if (err) throw err;
+  console.log('file saved');
 });
 ```
 
@@ -435,5 +428,4 @@ See [LICENSE.md](LICENSE.md).
 [dev-badge]: https://david-dm.org/zemirco/json2csv.svg
 [dev-badge-url]: https://david-dm.org/zemirco/json2csv
 [CHANGELOG]: CHANGELOG.md
-[Bluebird]: http://bluebirdjs.com/docs/api/promise.promisify.html
 [flat]: https://www.npmjs.com/package/flat
diff --git a/bin/json2csv.js b/bin/json2csv.js
@@ -13,8 +13,8 @@ var pkg = require('../package');
 
 program
   .version(pkg.version)
-  .option('-i, --input <input>', 'Path and name of the incoming json file.')
-  .option('-o, --output [output]', 'Path and name of the resulting csv file. Defaults to console.')
+  .option('-i, --input <input>', 'Path and name of the incoming json file. If not provided, will read from stdin.')
+  .option('-o, --output [output]', 'Path and name of the resulting csv file. Defaults to stdout.')
   .option('-f, --fields <fields>', 'Specify the fields to convert.')
   .option('-l, --fieldList [list]', 'Specify a file with a list of fields to include. One field per line.')
   .option('-d, --delimiter [delimiter]', 'Specify a delimiter other than the default comma to use.')
@@ -79,7 +79,7 @@ function getInput(callback) {
   });
 }
 
-function logPretty(csv, callback) {
+function logPretty(csv) {
   var lines = csv.split(os.EOL);
   var table = new Table({
     head: lines[0].split(','),
@@ -90,11 +90,8 @@ function logPretty(csv, callback) {
 
   for (var i = 1; i < lines.length; i++) {
     table.push(lines[i].split('","'));
-
-    if (i === lines.length - 1) {
-      callback(table.toString());
-    }
   }
+  return table.toString();
 }
 
 getFields(function (err, fields) {
@@ -129,30 +126,23 @@ getFields(function (err, fields) {
       opts.newLine = program.newLine;
     }
 
-    json2csv(opts, function (csvError, csv) {
-      if (csvError) {
-        debug(csvError);
-      }
-
-      if (program.output) {
-        fs.writeFile(program.output, csv, function (writeError) {
-          if (writeError) {
-            throw new Error('Cannot save to ' + program.output + ': ' + writeError);
-          }
+    var csv = json2csv(opts);
+    if (program.output) {
+      fs.writeFile(program.output, csv, function (writeError) {
+        if (writeError) {
+          throw new Error('Cannot save to ' + program.output + ': ' + writeError);
+        }
 
-          debug(program.input + ' successfully converted to ' + program.output);
-        });
+        debug(program.input + ' successfully converted to ' + program.output);
+      });
+    } else {
+      /*eslint-disable no-console */
+      if (program.pretty) {
+        console.log(logPretty(csv));
       } else {
-        /*eslint-disable no-console */
-        if (program.pretty) {
-          logPretty(csv, function (res) {
-            console.log(res);
-          });
-        } else {
-          console.log(csv);
-        }
-        /*eslint-enable no-console */
+        console.log(csv);
       }
-    });
+      /*eslint-enable no-console */
+    }
   });
 });
diff --git a/index.d.ts b/index.d.ts
@@ -25,7 +25,8 @@ declare namespace json2csv {
     (error: Error, csv: string): void;
   }
 
-  export function json2csv(options: IOptions, callback: ICallback): string;
+  export function json2csv(options: IOptions, callback: ICallback): void;
+  export function json2csv(options: IOptions): string;
 }
 
 export = json2csv.json2csv;
diff --git a/lib/json2csv.js b/lib/json2csv.js
@@ -6,41 +6,51 @@ var lodashGet = require('lodash.get');
 var flatten = require('flat');
 
 /**
- * Main function that converts json to csv
+ * Main function that converts json to csv.
  *
  * @param {Object} params Function parameters containing data, fields,
  * delimiter (default is ','), hasCSVColumnTitle (default is true)
  * and default value (default is '')
- * @param {Function} callback(err, csv) - Callback function
+ * @param {Function} [callback] Callback function
  *   if error, returning error in call back.
  *   if csv is created successfully, returning csv output to callback.
  */
 module.exports = function (params, callback) {
-  if (!callback || typeof callback !== 'function') {
-    throw new Error('Callback is required');
-  }
-
-  checkParams(params, function (err) {
-    if (err) {
-      return callback(err);
+  var hasCallback = typeof callback === 'function';
+
+  var err;
+  try {
+    checkParams(params);
+  } catch (err) {
+    if (hasCallback) {
+      return process.nextTick(function () {
+        callback(err);
+      });
+    } else {
+      throw err;
     }
-
-    var titles = createColumnTitles(params);
-    var csv = createColumnContent(params, titles);
-
-    callback(null, csv);
-  });
+  }
+  var titles = createColumnTitles(params);
+  var csv = createColumnContent(params, titles);
+  if (hasCallback) {
+    return process.nextTick(function () {
+      callback(null, csv);
+    });
+  } else {
+    return csv;
+  }
 };
 
 
 /**
- * Check passing params
+ * Check passing params.
+ *
+ * Note that this modifies params.
  *
  * @param {Object} params Function parameters containing data, fields,
  * delimiter, default value, mark quotes and hasCSVColumnTitle
- * @param {Function} callback Callback function returning error when invalid field is found
  */
-function checkParams(params, callback) {
+function checkParams(params) {
   params.data = params.data || [];
 
   // if data is an Object, not in array [{}], then just create 1 item array.
@@ -55,14 +65,14 @@ function checkParams(params, callback) {
 
   // Set params.fields default to first data element's keys
   if (!params.fields && (params.data.length === 0 || typeof params.data[0] !== 'object')) {
-    return callback(new Error('params should include "fields" and/or non-empty "data" array of objects'));
+    throw new Error('params should include "fields" and/or non-empty "data" array of objects');
   }
   params.fields = params.fields || Object.keys(params.data[0]);
 
 
   //#check fieldNames
   if (params.fieldNames && params.fieldNames.length !== params.fields.length) {
-    return callback(new Error('fieldNames and fields should be of the same length, if fieldNames is provided.'));
+    throw new Error('fieldNames and fields should be of the same length, if fieldNames is provided.');
   }
 
   // Get fieldNames from fields
@@ -93,8 +103,6 @@ function checkParams(params, callback) {
 
   //#check include empty rows, defaults to false
   params.includeEmptyRows = params.includeEmptyRows || false;
-
-  callback(null);
 }
 
 /**
@@ -188,7 +196,7 @@ function createColumnContent(params, str) {
           //JSON.stringify('\\') results in a string with two backslash
           //characters in it. I.e. '\\\\'.
           stringifiedElement = stringifiedElement.replace(/\\\\/g, '\\');
-          
+
           if (params.excelStrings && typeof val === 'string') {
             stringifiedElement = '"="' + stringifiedElement + '""';
           }

diff --git a/test/index.js b/test/index.js
@@ -22,16 +22,44 @@ async.parallel(loadFixtures(csvFixtures), function (err) {
     /*eslint-enable no-console*/
   }
 
-  test('should throw if no callback', function (t) {
-    t.throws(function () {
-      json2csv({
-        data: jsonDefault
-      });
-    }, /Callback is required/);
+  test('should work synchronously', function (t) {
+    var csv = json2csv({
+      data: jsonDefault
+    });
+    t.equal(csv, csvFixtures.default);
     t.end();
   });
 
-  test('should error if fieldNames don\'t line up to fields', function (t) {
+  test('should work asynchronously and not release zalgo', function (t) {
+    var releasedZalgo = true;
+    json2csv({
+      data: jsonDefault
+    }, function (err, csv) {
+      t.equal(csv, csvFixtures.default);
+      t.notOk(releasedZalgo);
+      t.end();
+    });
+
+    releasedZalgo = false;
+  });
+
+  test('should error synchronously if fieldNames don\'t line up to fields', function (t) {
+    var csv;
+    try {
+      csv = json2csv({
+        data: jsonDefault,
+        field: ['carModel'],
+        fieldNames: ['test', 'blah']
+      });
+      t.notOk(true);
+    } catch (error) {
+      t.equal(error.message, 'fieldNames and fields should be of the same length, if fieldNames is provided.');
+      t.notOk(csv);
+      t.end();
+    }
+  });
+
+  test('should error asynchronously if fieldNames don\'t line up to fields', function (t) {
     json2csv({
       data: jsonDefault,
       field: ['carModel'],
@@ -53,7 +81,6 @@ async.parallel(loadFixtures(csvFixtures), function (err) {
       t.end();
     });
   });
-
 
   test('should parse json to csv without fields', function (t) {
     json2csv({
@@ -364,7 +391,7 @@ async.parallel(loadFixtures(csvFixtures), function (err) {
       t.end();
     });
   });
-  
+
   test('should escape " when preceeded by \\', function (t){
     json2csv({
       data: [{field: '\\"'}]
@@ -374,7 +401,7 @@ async.parallel(loadFixtures(csvFixtures), function (err) {
       t.end();
     });
   });
-  
+
   test('should format strings to force excel to view the values as strings', function (t) {
     json2csv({
       data: jsonDefault,