feat: make evaluator config depend on the running env

README.md

@@ -55,7 +55,7 @@ Have you got suggestions for improvement? [I am all ears](https://github.com/gaj
 
 |Name|Description|Default value|
 |---|---|---|
-|`evaluator`|HTML parser and selector engine. Possible values: `cheerio`, `browser`. Use `cheerio` if you are running Surgeon in Node.js. Use `browser` if you are running Surgeon in a browser or headless browser (e.g. PhantomJS).|`cheerio`|
+|`evaluator`|HTML parser and selector engine. Possible values: `cheerio`, `browser`. Use `cheerio` if you are running Surgeon in Node.js. Use `browser` if you are running Surgeon in a browser or a headless browser (e.g. PhantomJS).|`browser` if `window` and `document` variables are present, `cheerio` otherwise.|
 
 ## Cookbook
 

src/factories/createConfiguration.js

@@ -8,13 +8,24 @@ import {
   browserEvaluator,
   cheerioEvaluator
 } from '../evaluators';
+import {
+  isEnvironmentBrowser
+} from '../utilities';
 
 export default (userConfiguration: UserConfigurationType = {}): ConfigurationType => {
   let evaluator;
 
-  if (!userConfiguration.evaluator || userConfiguration.evaluator === 'cheerio') {
+  let evaluatorName = userConfiguration.evaluator;
+
+  if (!evaluatorName) {
+    const environmentIsBrowser = isEnvironmentBrowser();
+
+    evaluatorName = environmentIsBrowser ? 'browser' : 'cheerio';
+  }
+
+  if (evaluatorName === 'cheerio') {
     evaluator = cheerioEvaluator();
-  } else if (userConfiguration.evaluator === 'browser') {
+  } else if (evaluatorName === 'browser') {
     evaluator = browserEvaluator();
   } else {
     throw new Error('Unknown adapter.');

src/utilities/index.js

@@ -6,12 +6,14 @@ import getQuantifier from './getQuantifier';
 import hasAttributeSelector from './hasAttributeSelector';
 import hasPropertySelector from './hasPropertySelector';
 import hasQuantifier from './hasQuantifier';
+import isEnvironmentBrowser from './isEnvironmentBrowser';
 
 export {
   getAttributeSelector,
   getPropertySelector,
   getQuantifier,
   hasAttributeSelector,
   hasPropertySelector,
-  hasQuantifier
+  hasQuantifier,
+  isEnvironmentBrowser
 };

src/utilities/isEnvironmentBrowser.js

@@ -0,0 +1,5 @@
+// @flow
+
+export default (): boolean => {
+  return typeof window === 'object' && typeof document === 'object';
+};