feat: Improve async promise to optionally not return (#421)

README.md

@@ -269,7 +269,7 @@ asyncParser.input.push(null); // Sending `null` to a stream signal that no more
 * `fromInput` allows you to set the input stream.
 * `throughTransform` allows you to add transforms to the stream.
 * `toOutput` allows you to set the output stream.
-* `promise` returns a promise that resolves when the stream ends or errors.
+* `promise` returns a promise that resolves when the stream ends or errors. Takes a boolean parameter to indicate if the resulting CSV should be kept in-memory and be resolved by the promise.
 
 ```js
 const { createReadStream, createWriteStream } = require('fs');
@@ -279,12 +279,23 @@ const fields = ['field1', 'field2', 'field3'];
 const opts = { fields };
 const transformOpts = { highWaterMark: 8192 };
 
+// Using the promise API
 const input = createReadStream(inputPath, { encoding: 'utf8' });
-const output = createWriteStream(outputPath, { encoding: 'utf8' });
 const asyncParser = new JSON2CSVAsyncParser(opts, transformOpts);
-asyncParser.fromInput(input).toOutput(output).promise()
+const parsingProcessor = asyncParser.fromInput(input);
+
+parsingProcessor.promise()
   .then(csv => console.log(csv))
-  .catch(err => console.error(err));;
+  .catch(err => console.error(err));
+
+// Using the promise API just to know when the process finnish
+// but not actually load the CSV in memory
+const input = createReadStream(inputPath, { encoding: 'utf8' });
+const output = createWriteStream(outputPath, { encoding: 'utf8' });
+const asyncParser = new JSON2CSVAsyncParser(opts, transformOpts);
+const parsingProcessor = asyncParser.fromInput(input).toOutput(output);
+
+parsingProcessor.promise(false).catch(err => console.error(err));
 ```
 
 you can also use the convenience method `parseAsync` which accept both JSON arrays/objects and readable streams and returns a promise.

lib/JSON2CSVAsyncParser.js

@@ -39,8 +39,15 @@ class JSON2CSVAsyncParser {
     return this;
   }
 
-  promise() {
+  promise(returnCSV = true) {
     return new Promise((resolve, reject) => {
+      if (!returnCSV) {
+        this.processor
+          .on('finish', () => resolve())
+          .on('error', err => reject(err));
+        return;
+      }
+
       let csvBuffer = [];
       this.processor
         .on('data', chunk => csvBuffer.push(chunk.toString()))

test/JSON2CSVAsyncParser.js

@@ -955,4 +955,34 @@ module.exports = (testRunner, jsonFixtures, csvFixtures, inMemoryJsonFixtures) =
     t.end();
   });
 
+  testRunner.add('should not return if ret option is set to false', (t) => {
+    const parser = new AsyncParser();
+    const configuredParser = parser.fromInput(jsonFixtures.default())
+    let csv = '';
+
+    configuredParser.processor.on('data', chunk => (csv += chunk.toString()));
+
+    configuredParser.promise(false)
+      .then(res => {
+        t.equal(res, undefined);
+        t.equal(csv, csvFixtures.defaultStream);
+      })
+      .catch(err => t.notOk(true, err.message))
+      .then(() => t.end());
+  });
+
+  testRunner.add('should catch errors even if ret option is set to false', (t) => {
+    const opts = {
+      fields: ['carModel', 'price', 'color', 'transmission']
+    };
+
+    const parser = new AsyncParser(opts);
+
+    parser.fromInput(jsonFixtures.defaultInvalid()).promise(false)
+      .then(() => t.notOk(true))
+      .catch(err => t.ok(err.message.includes('Invalid JSON')))
+      .then(() => t.end());
+  });
+
+
 };