When clicking <a> tag with no href, don't attempt navigation to "null". Fixes #943

src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Services/UriHelper.ts

@@ -19,9 +19,11 @@ registerFunction(`${registeredFunctionPrefix}.enableNavigationInterception`, ()
 
   document.addEventListener('click', event => {
     // Intercept clicks on all <a> elements where the href is within the <base href> URI space
-    const anchorTarget = findClosestAncestor(event.target as Element | null, 'A');
-    if (anchorTarget) {
-      const href = anchorTarget.getAttribute('href');
+    // We must explicitly check if it has an 'href' attribute, because if it doesn't, the result might be null or an empty string depending on the browser
+    const anchorTarget = findClosestAncestor(event.target as Element | null, 'A') as HTMLAnchorElement;
+    const hrefAttributeName = 'href';
+    if (anchorTarget && anchorTarget.hasAttribute(hrefAttributeName)) {
+      const href = anchorTarget.getAttribute(hrefAttributeName)!;
       const absoluteHref = toAbsoluteUri(href);
 
       // Don't stop ctrl/meta-click (etc) from opening links in new tabs/windows

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/RoutingTest.cs

@@ -231,6 +231,19 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             AssertHighlightedLinks("Other", "Other with base-relative URL (matches all)");
         }
 
+        [Fact]
+        public void ClickingAnchorWithNoHrefShouldNotNavigate()
+        {
+            SetUrlViaPushState($"{ServerPathBase}/");
+            var initialUrl = Browser.Url;
+
+            var app = MountTestComponent<TestRouter>();
+            app.FindElement(By.Id("anchor-with-no-href")).Click();
+
+            Assert.Equal(initialUrl, Browser.Url);
+            AssertHighlightedLinks("Default (matches all)", "Default with base-relative URL (matches all)");
+        }
+
         public void Dispose()
         {
             // Clear any existing state

test/testapps/BasicTestApp/RouterTest/Links.cshtml

@@ -16,3 +16,7 @@
 <button onclick=@(x => uriHelper.NavigateTo("Other"))>
     Programmatic navigation
 </button>
+
+<a id="anchor-with-no-href">
+    Anchor tag with no href attribute
+</a>