1 files changed, 82 insertions, 6 deletions
diff --git a/lib/reduce.js b/lib/reduce.js
index d13ace0..feaa959 100644
--- a/lib/reduce.js
+++ b/lib/reduce.js
@@ -35,14 +35,90 @@ import awaitify from './internal/awaitify'
  * @returns {Promise} a promise, if no callback is passed
  * @example
  *
- * async.reduce([1,2,3], 0, function(memo, item, callback) {
- *     // pointless async:
- *     process.nextTick(function() {
- *         callback(null, memo + item)
+ * // file1.txt is a file that is 1000 bytes in size
+ * // file2.txt is a file that is 2000 bytes in size
+ * // file3.txt is a file that is 3000 bytes in size
+ * // file4.txt does not exist
+ *
+ * const fileList = ['file1.txt','file2.txt','file3.txt'];
+ * const withMissingFileList = ['file1.txt','file2.txt','file3.txt', 'file4.txt'];
+ *
+ * // asynchronous function that computes the file size in bytes
+ * // file size is added to the memoized value, then returned
+ * function getFileSizeInBytes(memo, file, callback) {
+ *     fs.stat(file, function(err, stat) {
+ *         if (err) {
+ *             return callback(err);
+ *         }
+ *         callback(null, memo + stat.size);
  *     });
- * }, function(err, result) {
- *     // result is now equal to the last value of memo, which is 6
+ * }
+ *
+ * // Using callbacks
+ * async.reduce(fileList, 0, getFileSizeInBytes, function(err, result) {
+ *     if (err) {
+ *         console.log(err);
+ *     } else {
+ *         console.log(result);
+ *         // 6000
+ *         // which is the sum of the file sizes of the three files
+ *     }
+ * });
+ *
+ * // Error Handling
+ * async.reduce(withMissingFileList, 0, getFileSizeInBytes, function(err, result) {
+ *     if (err) {
+ *         console.log(err);
+ *         // [ Error: ENOENT: no such file or directory ]
+ *     } else {
+ *         console.log(result);
+ *     }
+ * });
+ *
+ * // Using Promises
+ * async.reduce(fileList, 0, getFileSizeInBytes)
+ * .then( result => {
+ *     console.log(result);
+ *     // 6000
+ *     // which is the sum of the file sizes of the three files
+ * }).catch( err => {
+ *     console.log(err);
+ * });
+ *
+ * // Error Handling
+ * async.reduce(withMissingFileList, 0, getFileSizeInBytes)
+ * .then( result => {
+ *     console.log(result);
+ * }).catch( err => {
+ *     console.log(err);
+ *     // [ Error: ENOENT: no such file or directory ]
  * });
+ *
+ * // Using async/await
+ * async () => {
+ *     try {
+ *         let result = await async.reduce(fileList, 0, getFileSizeInBytes);
+ *         console.log(result);
+ *         // 6000
+ *         // which is the sum of the file sizes of the three files
+ *     }
+ *     catch (err) {
+ *         console.log(err);
+ *     }
+ * }
+ *
+ * // Error Handling
+ * async () => {
+ *     try {
+ *         let result = await async.reduce(withMissingFileList, 0, getFileSizeInBytes);
+ *         console.log(result);
+ *     }
+ *     catch (err) {
+ *         console.log(err);
+ *         // [ Error: ENOENT: no such file or directory ]
+ *     }
+ * }
+ *
  */
 function reduce(coll, memo, iteratee, callback) {
     callback = once(callback);