Customize blade directive to allow changing the div id

src/BladeDirective.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Inertia;
+
+class BladeDirective
+{
+    public function render(string $id = 'app')
+    {
+        return new class($id) {
+            private $id;
+
+            private $page;
+
+            public function __construct(string $id)
+            {
+                $this->id = $id;
+            }
+
+            public function withPage($page)
+            {
+                $this->page = $page;
+
+                return $this;
+            }
+
+            public function __toString()
+            {
+                return '<div id="'.$this->id.'" data-page="'.e(json_encode($this->page)).'"></div>';
+            }
+        };
+    }
+}

src/ServiceProvider.php

@@ -12,6 +12,7 @@ class ServiceProvider extends BaseServiceProvider
     public function register()
     {
         $this->app->singleton(ResponseFactory::class);
+        $this->app->singleton(BladeDirective::class);
     }
 
     public function boot()
@@ -24,8 +25,8 @@ public function boot()
 
     protected function registerBladeDirective()
     {
-        Blade::directive('inertia', function () {
-            return '<div id="app" data-page="{{ json_encode($page) }}"></div>';
+        Blade::directive('inertia', function ($expression = '') {
+            return '<?php echo app(\Inertia\BladeDirective::class)->render('.$expression.')->withPage($page); ?>';
         });
     }
 

tests/BladeDirectiveTest.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Inertia\Tests;
+
+use Illuminate\Filesystem\Filesystem;
+use Illuminate\Support\Facades\Blade;
+use Illuminate\View\Compilers\BladeCompiler;
+use Mockery as m;
+
+class BladeDirectiveTest extends TestCase
+{
+    protected function compileBlade(string $expression, $page = ['foo' => 'bar'])
+    {
+        $compiler = new BladeCompiler(m::mock(Filesystem::class), __DIR__);
+        $compiler->directive('inertia', Blade::getCustomDirectives()['inertia']);
+
+        $compiled = tap($compiler->compileString($expression), function () {
+            m::close();
+        });
+
+        ob_start(function () {
+            // This closure exists to prevent 'eval' output from getting sent to
+            // STDOUT, which in turn causes PHPUnit to complain about it.
+            return '';
+        });
+
+        eval("?>$compiled<?php ");
+
+        return ob_get_flush();
+    }
+
+    public function test_directive_is_rendered_with_the_default_options()
+    {
+        $this->assertSame(
+            '<div id="app" data-page="{&quot;foo&quot;:&quot;bar&quot;}"></div>',
+            $this->compileBlade('@inertia')
+        );
+    }
+
+    public function test_directive_is_rendered_with_a_custom_div_id()
+    {
+        $this->assertSame(
+            '<div id="foo" data-page="{&quot;foo&quot;:&quot;bar&quot;}"></div>',
+            $this->compileBlade("@inertia('foo')")
+        );
+    }
+
+    public function test_directive_is_rendered_with_a_custom_div_id_with_shorthand_if_expression()
+    {
+        $this->assertSame(
+            '<div id="foo" data-page="{&quot;foo&quot;:&quot;bar&quot;}"></div>',
+            $this->compileBlade("@inertia(true ? 'foo' : 'bar')")
+        );
+    }
+}

tests/ServiceProviderTest.php

@@ -13,7 +13,9 @@ public function test_blade_directive_is_registered()
         $directives = Blade::getCustomDirectives();
 
         $this->assertArrayHasKey('inertia', $directives);
-        $this->assertEquals('<div id="app" data-page="{{ json_encode($page) }}"></div>', $directives['inertia']());
+
+        $this->assertEquals('<?php echo app(\Inertia\BladeDirective::class)->render()->withPage($page); ?>', $directives['inertia']());
+        $this->assertEquals('<?php echo app(\Inertia\BladeDirective::class)->render("foo")->withPage($page); ?>', $directives['inertia']('"foo"'));
     }
 
     public function test_request_macro_is_registered()