Add evaluate() function

README.md

@@ -386,6 +386,16 @@ Browsershot also can get the body of an html page after JavaScript has been exec
 Browsershot::url('https://example.com')->bodyHtml(); // returns the html of the body
 ```
 
+### Evaluate
+
+Browsershot can get the evaluation of an html page:
+
+```php
+Browsershot::url('https://example.com')
+  ->deviceScaleFactor(2)
+  ->evaluate("window.devicePixelRatio"); // returns 2
+```
+
 ### Misc
 
 #### Setting an arbitrary option

bin/browser.js

@@ -2,6 +2,20 @@ const puppeteer = require('puppeteer');
 
 const request = JSON.parse(process.argv[2]);
 
+const getOutput = async (page, request) => {
+    let output;
+
+    if (request.action == 'evaluate') {
+        output = await page.evaluate(request.options.pageFunction);
+
+        return output;
+    }
+
+    output = await page[request.action](request.options);
+
+    return output.toString('base64');
+};
+
 const callChrome = async () => {
     let browser;
     let page;
@@ -73,10 +87,10 @@ const callChrome = async () => {
             request.options.clip = await element.boundingBox();
         }
 
-        output = await page[request.action](request.options);
+        output = await getOutput(page, request);
 
         if (!request.options.path) {
-            console.log(output.toString('base64'));
+            console.log(output);
         }
 
         await browser.close();

src/Browsershot.php

@@ -414,6 +414,13 @@ public function savePdf(string $targetPath)
         }
     }
 
+    public function evaluate(string $pageFunction): string
+    {
+        $command = $this->createEvaluateCommand($pageFunction);
+
+        return $this->callBrowser($command);
+    }
+
     public function applyManipulations(string $imagePath)
     {
         Image::load($imagePath)
@@ -471,6 +478,17 @@ public function createPdfCommand($targetPath = null): array
         return $command;
     }
 
+    public function createEvaluateCommand(string $pageFunction): array
+    {
+        $url = $this->html ? $this->createTemporaryHtmlFile() : $this->url;
+
+        $options = [
+            'pageFunction' => $pageFunction,
+        ];
+
+        return $this->createCommand($url, 'evaluate', $options);
+    }
+
     protected function getOptionArgs(): array
     {
         $args = [];
@@ -537,7 +555,7 @@ protected function callBrowser(array $command)
         $process->run();
 
         if ($process->isSuccessful()) {
-            return $process->getOutput();
+            return rtrim($process->getOutput());
         }
 
         if ($process->getExitCode() === 2) {

tests/BrowsershotTest.php

@@ -814,4 +814,13 @@ public function it_can_click_on_the_page()
             ],
         ], $command);
     }
+
+    /** @test */
+    public function it_can_evaluate_page()
+    {
+        $result = Browsershot::url('https://example.com')
+            ->evaluate('1 + 1');
+
+        $this->assertEquals('2', $result);
+    }
 }