single extractor: returning undefined from output() omits value from result object

Author: 75lb

index.js

@@ -45,6 +45,8 @@ class CommandLineArgs {
         } else {
           extraction = fromTo(this.argv, { from: def.from, to, remove: true })
         }
+        result[def.name] = await def.output(extraction)
+
       } else if (def.extractor === 'single') {
         if (def.repeatable) {
           extraction = []
@@ -60,10 +62,13 @@ class CommandLineArgs {
         } else {
           extraction = single(this.argv, def.single, { remove: true })
         }
+        const output = await def.output(extraction)
+        if (output !== undefined) {
+          result[def.name] = output
+        }
       } else {
         throw new Error('Extractor not found: ' + def.extractor)
       }
-      result[def.name] = await def.output(extraction)
     }
 
     /* Do the positionals backwards, so removing them doesn't mess up the position config */

test/test.js

@@ -42,14 +42,14 @@ test.set('--option <no value>', async function () {
   a.deepEqual(cla.argv, ['one', 'two', '--two', 'three'])
 })
 
-test.set('single --option flag', async function () {
+test.set('single --option flag, value set', async function () {
   const argv = ['one', 'two', '--one', '--two']
   const optionDefinitions = [
     {
       name: 'one',
       extractor: 'single',
       single: '--one',
-      output: extraction => true
+      output: extraction => extraction.length === 1 ? true : undefined
     }
   ]
   const cla = new CommandLineArgs(argv)
@@ -58,6 +58,38 @@ test.set('single --option flag', async function () {
   a.deepEqual(cla.argv, ['one', 'two', '--two'])
 })
 
+test.set('single --option flag, value set not, output returns false', async function () {
+  const argv = ['one', 'two', '--two']
+  const optionDefinitions = [
+    {
+      name: 'one',
+      extractor: 'single',
+      single: '--one',
+      output: extraction => extraction.length === 1
+    }
+  ]
+  const cla = new CommandLineArgs(argv)
+  const result = await cla.parse(optionDefinitions)
+  a.deepEqual(result, { one: false })
+  a.deepEqual(cla.argv, ['one', 'two', '--two'])
+})
+
+test.set('single --option flag, not set. Returning undefined omits option from result.', async function () {
+  const argv = ['one', 'two', '--two']
+  const optionDefinitions = [
+    {
+      name: 'one',
+      extractor: 'single',
+      single: '--one',
+      output: extraction => extraction.length === 1 ? true : undefined
+    }
+  ]
+  const cla = new CommandLineArgs(argv)
+  const result = await cla.parse(optionDefinitions)
+  a.deepEqual(result, {})
+  a.deepEqual(cla.argv, ['one', 'two', '--two'])
+})
+
 test.set('single regex', async function () {
   const argv = ['one', 'two', '--one', '--two']
   const optionDefinitions = [