feat(join): Flatten before joining

Author: justinvdm

internal/flatten.js

@@ -0,0 +1,20 @@
+var isArray = Array.isArray
+
+module.exports = function flatten(vals) {
+  var result = []
+  var n = vals.length
+  var i = -1
+  var val
+
+  while (++i < n) {
+    val = vals[i]
+
+    if (isArray(val)) {
+      result.push.apply(result, flatten(val))
+    } else {
+      result.push(val)
+    }
+  }
+
+  return result
+}

join.js

@@ -1,11 +1,12 @@
 var tuple = require('./tuple')
+var flatten = require('./internal/flatten')
 
 function join(a, b, c) {
   return b != null && c == null ? joinCurried(a, b) : joinMain(a, b, c)
 }
 
 function joinMain(id, joiner, makerFns) {
-  var result = tuple(id, makerFns)
+  var result = flatten(tuple(id, makerFns))
   return typeof joiner === 'function' ? joiner(result) : result.join(joiner)
 }
 

tests/internal/flatten.test.js

@@ -0,0 +1,12 @@
+const tap = require('tap')
+const flatten = require('../../internal/flatten')
+
+tap.test('flatten', t => {
+  t.deepEquals(flatten([[1, [2, [[3], [[[4]]]]]]]), [1, 2, 3, 4])
+  t.end()
+})
+
+tap.test('empty items', t => {
+  t.deepEquals(flatten([2, [], 3]), [2, 3])
+  t.end()
+})

tests/join.test.js

@@ -6,3 +6,9 @@ tap.test('function as joiner', t => {
   t.equals(result, 'a b')
   t.end()
 })
+
+tap.test('flattening results', t => {
+  const result = join(23, ' ', [() => 'a', () => ['b', ['c']]])
+  t.equals(result, 'a b c')
+  t.end()
+})