Added serializer to helpers

index.js

@@ -4,11 +4,12 @@ exports.getValue = require('./lib/getValue')
 exports.isObject = require('./lib/isObject')
 exports.merge = require('./lib/merge')
 exports.parseQueryString = require('./lib/parseQueryString')
+exports.serializer = require('./lib/serializer')
+exports.splitStringIntoChunks = require('./lib/splitStringIntoChunks')
 exports.strPad = require('./lib/strPad')
 exports.trim = require('./lib/trim')
-exports.unique = require('./lib/unique')
-exports.splitStringIntoChunks = require('./lib/splitStringIntoChunks')
 exports.typecastString = require('./lib/typecastString')
+exports.unique = require('./lib/unique')
 
 exports.config = require('./lib/config').config
 exports.Config = require('./lib/config').default

lib/serializer.js

@@ -0,0 +1,34 @@
+/**
+ * Serializer creates a pipe of consequent promises, resolving with the values
+ * of each successful promise or rejecting with the last error
+ *
+ * @param { array } data              Segments for each promise
+ * @param { function } fn             Serializer function
+ * @return { Promise }                Promise
+ */
+module.exports = function serializer (tasks, fn) {
+  tasks = tasks.slice()
+  let i = 0
+  const values = []
+
+  return new Promise((resolve, reject) => {
+    const serializer = () => {
+      if (!tasks.length) {
+        return resolve(values)
+      }
+
+      const task = tasks.splice(0, 1)[0]
+
+      Promise.resolve(fn(task, i++))
+        .then((response) => {
+          values.push(response)
+          serializer()
+        })
+        .catch((err) => {
+          reject(err)
+        })
+    }
+
+    serializer()
+  })
+}

tests/serializer.js

@@ -0,0 +1,50 @@
+const expect = require('expect.js')
+const serializer = require('../lib/serializer')
+
+describe('serializer', () => {
+  it('should return a promise', (done) => {
+    expect(serializer([])).to.be.a(Promise)
+    done()
+  })
+
+  it('should resolve the promises in chain and return all the resolved values as an array', (done) => {
+    const data = [0, 1, 2, 3]
+
+    serializer(data, (item, i) => {
+      if (item !== data[i]) {
+        return Promise.reject(new Error('Did not loop in chain'))
+      }
+
+      return Promise.resolve(item)
+    })
+      .then((response) => {
+        expect(response).to.eql(data)
+        done()
+      })
+      .catch(done)
+  })
+
+  it('should stop the serializer chain when callback rejects', (done) => {
+    const data = [0, 1, 2, 3]
+    let counter = 0
+
+    serializer(data, (item, i) => {
+      if (i === 2) {
+        return Promise.reject(new Error('Rejecting on purpose'))
+      }
+
+      counter++
+    })
+      .then(() => {
+        done(new Error('Should have rejected the chain'))
+      })
+      .catch((err) => {
+        if (counter !== 2) {
+          err.message = 'Counter mismatch'
+          return done(err)
+        }
+
+        done()
+      })
+  })
+})