Implement Page.GetElementAsync (a.k.a Page.$eval) (#189)

Author: Meir017

lib/PuppeteerSharp.Tests/Page/EvalTests.cs

@@ -0,0 +1,42 @@
+using System.Threading.Tasks;
+using Xunit;
+
+namespace PuppeteerSharp.Tests.Page
+{
+    [Collection("PuppeteerLoaderFixture collection")]
+    public class EvalTests : PuppeteerPageBaseTest
+    {
+        [Fact]
+        public async Task ShouldWork()
+        {
+            await Page.SetContentAsync("<section id='testAttribute'>43543</section>");
+            var idAttribute = await Page.GetElementAsync("section").EvaluateFunctionAsync<string>("e => e.id");
+            Assert.Equal("testAttribute", idAttribute);
+        }
+
+        [Fact]
+        public async Task ShouldAcceptArguments()
+        {
+            await Page.SetContentAsync("<section>hello</section>");
+            var text = await Page.GetElementAsync("section").EvaluateFunctionAsync<string>("(e, suffix) => e.textContent + suffix", " world!");
+            Assert.Equal("hello world!", text);
+        }
+
+        [Fact]
+        public async Task ShouldAcceptElementHandlesAsArguments()
+        {
+            await Page.SetContentAsync("<section>hello</section><div> world</div>");
+            var divHandle = await Page.GetElementAsync("div");
+            var text = await Page.GetElementAsync("section").EvaluateFunctionAsync<string>("(e, div) => e.textContent + div.textContent", divHandle);
+            Assert.Equal("hello world", text);
+        }
+
+        [Fact]
+        public async Task ShouldThrowErrorIfNoElementIsFound()
+        {
+            var exception = await Assert.ThrowsAsync<SelectorException>(()
+                => Page.GetElementAsync("section").EvaluateFunctionAsync<string>("e => e.id"));
+            Assert.Contains("failed to find element matching selector", exception.Message);
+        }
+    }
+}

lib/PuppeteerSharp/ElementHandle.cs

@@ -7,12 +7,12 @@ namespace PuppeteerSharp
 {
     public class ElementHandle : JSHandle
     {
-        private readonly Page _page;
+        internal Page Page { get; }
 
         public ElementHandle(ExecutionContext context, Session client, object remoteObject, Page page) :
             base(context, client, remoteObject)
         {
-            _page = page;
+            Page = page;
         }
 
         public override ElementHandle AsElement() => this;
@@ -24,7 +24,7 @@ public ElementHandle(ExecutionContext context, Session client, object remoteObje
         public async Task HoverAsync()
         {
             var (x, y) = await VisibleCenterAsync();
-            await _page.Mouse.MoveAsync(x, y);
+            await Page.Mouse.MoveAsync(x, y);
         }
 
         /// <summary>
@@ -36,7 +36,7 @@ public async Task HoverAsync()
         public async Task ClickAsync(ClickOptions options = null)
         {
             var (x, y) = await VisibleCenterAsync();
-            await _page.Mouse.ClickAsync(x, y, options);
+            await Page.Mouse.ClickAsync(x, y, options);
         }
 
         /// <summary>
@@ -60,7 +60,7 @@ public async Task UploadFileAsync(params string[] filePaths)
         public async Task TapAsync()
         {
             var (x, y) = await VisibleCenterAsync();
-            await _page.Touchscreen.TapAsync(x, y);
+            await Page.Touchscreen.TapAsync(x, y);
         }
 
         /// <summary>
@@ -93,7 +93,7 @@ public async Task TapAsync()
         public async Task TypeAsync(string text, TypeOptions options = null)
         {
             await FocusAsync();
-            await _page.Keyboard.TypeAsync(text, options);
+            await Page.Keyboard.TypeAsync(text, options);
         }
 
         /// <summary>
@@ -108,7 +108,7 @@ public async Task TypeAsync(string text, TypeOptions options = null)
         public async Task PressAsync(string key, PressOptions options = null)
         {
             await FocusAsync();
-            await _page.Keyboard.PressAsync(key, options);
+            await Page.Keyboard.PressAsync(key, options);
         }
 
         internal async Task<ElementHandle> GetElementAsync(string selector)

lib/PuppeteerSharp/Extensions.cs

@@ -0,0 +1,32 @@
+using System.Threading.Tasks;
+
+namespace PuppeteerSharp
+{
+    public static class Extensions
+    {
+        /// <summary>
+        /// Runs <paramref name="pageFunction"/> within the frame and passes it the outcome of <paramref name="elementHandleTask"/> as the first argument
+        /// </summary>
+        /// <typeparam name="T">The type of the response</typeparam>
+        /// <param name="elementHandleTask">A task that returns an <see cref="ElementHandle"/> that will be used as the first argument in <paramref name="pageFunction"/></param>
+        /// <param name="pageFunction">Function to be evaluated in browser context</param>
+        /// <param name="args">Arguments to pass to <c>pageFunction</c></param>
+        /// <returns>Task which resolves to the return value of <c>pageFunction</c></returns>
+        /// <exception cref="SelectorException">If <paramref name="elementHandleTask"/> resolves to <c>null</c></exception>
+        public static async Task<T> EvaluateFunctionAsync<T>(this Task<ElementHandle> elementHandleTask, string pageFunction, params object[] args)
+        {
+            var elementHandle = await elementHandleTask;
+            if (elementHandle == null)
+            {
+                throw new SelectorException($"Error: failed to find element matching selector");
+            }
+
+            var newArgs = new object[args.Length + 1];
+            newArgs[0] = elementHandle;
+            args.CopyTo(newArgs, 1);
+            var result = await elementHandle.Page.EvaluateFunctionAsync<T>(pageFunction, newArgs);
+            await elementHandle.DisposeAsync();
+            return result;
+        }
+    }
+}

lib/PuppeteerSharp/Frame.cs

@@ -128,17 +128,7 @@ internal async Task<ElementHandle> GetElementAsync(string selector)
             var value = await document.GetElementAsync(selector);
             return value;
         }
-
-        internal Task<object> Eval(string selector, Func<object> pageFunction, object[] args)
-        {
-            throw new NotImplementedException();
-        }
-
-        internal Task<object> Eval(string selector, string pageFunction, object[] args)
-        {
-            throw new NotImplementedException();
-        }
-
+        
         internal Task<object> EvalMany(string selector, Func<object> pageFunction, object[] args)
         {
             throw new NotImplementedException();

lib/PuppeteerSharp/Page.cs

@@ -230,12 +230,6 @@ public async Task<JSHandle> QueryObjects(JSHandle prototypeHandle)
             return await context.QueryObjects(prototypeHandle);
         }
 
-        public async Task<object> EvalAsync(string selector, Func<object> pageFunction, params object[] args)
-            => await MainFrame.Eval(selector, pageFunction, args);
-
-        public async Task<object> EvalAsync(string selector, string pageFunction, params object[] args)
-            => await MainFrame.Eval(selector, pageFunction, args);
-
         public async Task SetRequestInterceptionAsync(bool value)
             => await _networkManager.SetRequestInterceptionAsync(value);
 

lib/PuppeteerSharp/SelectorException.cs

@@ -7,6 +7,10 @@ public class SelectorException : PuppeteerException
     {
         public string Selector { get; }
 
+        public SelectorException(string message) : base(message)
+        {
+        }
+
         public SelectorException(string message, string selector) : base(message)
         {
             Selector = selector;