Merge pull request #19 from github/no-then

No Promise.then

Author: josh

docs/rules/no-then.md

@@ -0,0 +1,31 @@
+# No `Promise.then`
+
+Yes, you should use promises, but prefer `async`/`await` syntax instead of `Promise.then()` callback chaining.
+
+``` js
+// bad
+function getProcessedData(url) {
+  return downloadData(url)
+    .catch(e => {
+      return downloadFallbackData(url)
+    })
+    .then(v => {
+      return processDataInWorker(v)
+    })
+}
+
+// good
+async function getProcessedData(url) {
+  let v
+  try {
+    v = await downloadData(url)
+  } catch(e) {
+    v = await downloadFallbackData(url)
+  }
+  return processDataInWorker(v)
+}
+```
+
+## See Also
+
+https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function

lib/configs/es6.js

@@ -13,6 +13,7 @@ module.exports = {
   ],
   'rules': {
     'github/array-foreach': 'error',
+    'github/no-then': 'error',
     'import/default': 'error',
     'import/export': 'error',
     'import/first': 'error',

lib/rules/no-then.js

@@ -0,0 +1,11 @@
+module.exports = function(context) {
+  return {
+    MemberExpression: function(node) {
+      if (node.property && node.property.name === 'then') {
+        context.report(node.property, 'Prefer async/await to Promise.then()')
+      } else if (node.property && node.property.name === 'catch') {
+        context.report(node.property, 'Prefer async/await to Promise.catch()')
+      }
+    }
+  }
+}

tests/no-then.js

@@ -0,0 +1,39 @@
+var rule = require('../lib/rules/no-then')
+var RuleTester = require('eslint').RuleTester
+
+var ruleTester = new RuleTester()
+
+ruleTester.run('no-then', rule, {
+  valid: [
+    {
+      code: '(async function() { const data = await read(); console.log(data) })()',
+      parserOptions: {ecmaVersion: 2017}
+    },
+    {
+      code: '(async function() { try { await read() } catch(error) { console.error(error) } })()',
+      parserOptions: {ecmaVersion: 2017}
+    }
+  ],
+  invalid: [
+    {
+      code: '(function() { read().then(data => console.log(data)) })()',
+      parserOptions: {ecmaVersion: 2017},
+      errors: [
+        {
+          message: 'Prefer async/await to Promise.then()',
+          type: 'Identifier'
+        }
+      ]
+    },
+    {
+      code: '(function() { read().catch(error => console.error(error)) })()',
+      parserOptions: {ecmaVersion: 2017},
+      errors: [
+        {
+          message: 'Prefer async/await to Promise.catch()',
+          type: 'Identifier'
+        }
+      ]
+    }
+  ]
+})