WaitForSelectorOptions and WaitForFunctionOptions add new TimeoutReturnsNull option

lib/PuppeteerSharp.Tests/WaitTaskTests/FrameWaitForSelectorTests.cs

@@ -208,6 +208,15 @@ public async Task ShouldRespectTimeout()
             Assert.Equal("waiting for function failed: timeout 10 ms exceeded", exception.Message);
         }
 
+        [PuppeteerTest("waittask.spec.ts", "Frame.waitForSelector", "should respect timeout")]
+        [PuppeteerFact]
+        public async Task ShouldRespectTimeoutReturnNull()
+        {
+            var result = await DevToolsContext.WaitForExpressionAsync("false", new WaitForFunctionOptions { Timeout = 10, TimeoutReturnsNull = true });
+
+            Assert.Null(result);
+        }
+
         [PuppeteerTest("waittask.spec.ts", "Frame.waitForSelector", "should have an error message specifically for awaiting an element to be hidden")]
         [PuppeteerFact]
         public async Task ShouldHaveAnErrorMessageSpecificallyForAwaitingAnElementToBeHidden()

lib/PuppeteerSharp/DOMWorld.cs

@@ -364,6 +364,7 @@ internal async Task<JSHandle> WaitForFunctionAsync(string script, WaitForFunctio
                  options.Polling,
                  options.PollingInterval,
                  options.Timeout ?? _timeoutSettings.Timeout,
+                 options.TimeoutReturnsNull,
                  args);
 
             return await waitTask
@@ -380,7 +381,8 @@ internal async Task<JSHandle> WaitForExpressionAsync(string script, WaitForFunct
                 "function",
                 options.Polling,
                 options.PollingInterval,
-                options.Timeout ?? _timeoutSettings.Timeout);
+                options.Timeout ?? _timeoutSettings.Timeout,
+                options.TimeoutReturnsNull);
 
             return await waitTask
                 .Task
@@ -437,6 +439,7 @@ function hasVisibleBoundingBox() {
                 polling,
                 null,
                 timeout,
+                options.TimeoutReturnsNull,
                 new object[] { selectorOrXPath, isXPath, options.Visible, options.Hidden });
 
             var handle = await waitTask.Task.ConfigureAwait(false);

lib/PuppeteerSharp/WaitForFunctionOptions.cs

@@ -14,6 +14,12 @@ public class WaitForFunctionOptions
         /// </summary>
         public int? Timeout { get; set; }
 
+        /// <summary>
+        /// If set to <see langword="true" />, the method will return <see langword="null"/> if the timeout is reached.
+        /// The default (<see langword="false" />) will throw a <see cref="WaitTaskTimeoutException"/> if the timeout is reached."/>
+        /// </summary>
+        public bool TimeoutReturnsNull { get; set; } = false;
+
         /// <summary>
         /// An interval at which the <c>pageFunction</c> is executed. defaults to <see cref="WaitForFunctionPollingOption.Raf"/>
         /// </summary>

lib/PuppeteerSharp/WaitForSelectorOptions.cs

@@ -14,6 +14,12 @@ public class WaitForSelectorOptions
         /// </summary>
         public int? Timeout { get; set; }
 
+        /// <summary>
+        /// If set to <see langword="true" />, the method will return <see langword="null"/> if the timeout is reached.
+        /// The default (<see langword="false" />) will throw a <see cref="WaitTaskTimeoutException"/> if the timeout is reached."/>
+        /// </summary>
+        public bool TimeoutReturnsNull { get; set; } = false;
+
         /// <summary>
         /// Wait for element to be present in DOM and to be visible.
         /// </summary>

lib/PuppeteerSharp/WaitTask.cs

@@ -14,6 +14,7 @@ internal class WaitTask : IDisposable
         private readonly int _timeout;
         private readonly object[] _args;
         private readonly string _title;
+        private readonly bool _timeoutReturnsNull;
         private readonly Task _timeoutTimer;
 
         private readonly CancellationTokenSource _cts;
@@ -107,6 +108,7 @@ internal WaitTask(
             WaitForFunctionPollingOption polling,
             int? pollingInterval,
             int timeout,
+            bool timeoutReturnsNull,
             object[] args = null)
         {
             if (string.IsNullOrEmpty(predicateBody))
@@ -125,6 +127,7 @@ internal WaitTask(
             _timeout = timeout;
             _args = args ?? Array.Empty<object>();
             _title = title;
+            _timeoutReturnsNull = timeoutReturnsNull;
 
             _cts = new CancellationTokenSource();
 
@@ -136,7 +139,7 @@ internal WaitTask(
             {
                 _timeoutTimer = System.Threading.Tasks.Task.Delay(timeout, _cts.Token)
                     .ContinueWith(
-                        _ => Terminate(new WaitTaskTimeoutException(timeout, title)),
+                        _ => Terminate(_timeoutReturnsNull ? null : new WaitTaskTimeoutException(timeout, title)),
                         TaskScheduler.Default);
             }
 
@@ -212,7 +215,16 @@ await _world.EvaluateFunctionAsync<bool>("s => !s", success)
         internal void Terminate(Exception exception)
         {
             _terminated = true;
-            _taskCompletion.TrySetException(exception);
+
+            if (exception == null)
+            {
+                _taskCompletion.TrySetResult(null);
+            }
+            else
+            {
+                _taskCompletion.TrySetException(exception);
+            }
+
             Cleanup();
         }