![]() Here’s how a page loads a script with defer, put in the head tag: The script is fetched asynchronously, and when it’s ready the HTML parsing is paused to execute the script, then it’s resumed. Here’s how a page loads a script with async, put in the head tag: Parsing is done before the script is even downloaded, so the page appears to the user way before the previous example. The parsing is done without any pauses, and when it finishes, the script is fetched, and executed. Here’s how a page loads a script without defer or async, put at the end of the body tag, just before it closes: The parsing is paused until the script is fetched, and executed. Here’s how a page loads a script without either defer or async, put in the head portion of the page: Performance comparison No defer or async, in the head These attributes only make sense when using the script in the head portion of the page, and they are useless if you put the script in the body footer like we saw above. The code doesn't create an infinite loop because StateHasChanged is only called when data is null.If you specify both, async takes precedence on modern browsers, while older browsers that support defer but not async will fallback to defer.įor the support table, check for async and for defer StateHasChanged is called to rerender the component with the new state obtained from the JS interop call (for more information, see ASP.NET Core Razor component rendering). Where JSRuntime.InvokeAsync is called, the ElementReference is only used in OnAfterRenderAsync and not in any earlier lifecycle method because there's no JS element until after the component is rendered. For more information, see ASP.NET Core Blazor JavaScript interoperability (JS interop). Directly modifying the DOM with JS isn't recommended in most scenarios because JS can interfere with Blazor's change tracking. The preceding example modifies the Document Object Model (DOM) directly for demonstration purposes only. The function is called with JSRuntimeExtensions.InvokeVoidAsync and doesn't return a value. While an app is prerendering, certain actions, such as calling into JavaScript (JS), aren't possible.įor the following example, the setElementText1 function is placed inside the element. Prerendering is covered in Prerender and integrate ASP.NET Core Razor components. This section applies to Blazor Server and hosted Blazor WebAssembly apps that prerender Razor components. Public void Dispose() => jsClass?.Dispose() įor dynamic content generation with BuildRenderTree, use the attribute: The JS function accepts a byte array from a C# method, decodes the array, and returns the text to the component for display. The example demonstrates how to invoke a JS function from a C# method that offloads a requirement from developer code to an existing JS API. The following example is based on TextDecoder, a JS-based decoder. For more information, see the Prerendering section. InvokeAsync unwraps the Promise and returns the value awaited by the Promise.įor Blazor apps with prerendering enabled, calling into JS isn't possible during prerendering. A JS Promise is returned for InvokeAsync methods.NET type that best maps to the JSON type returned. The TValue return type must also be JSON serializable.TimeSpan represents a time limit for a JS operation.The cancellation token ( CancellationToken) propagates a notification that operations should be canceled.Pass any number of JSON-serializable arguments in Object to a JS function.There's no need to register the function before it's called. To call, the identifier is someScope.someFunction. The function identifier ( String) is relative to the global scope ( window).NET, inject the IJSRuntime abstraction and call one of the following methods:įor the preceding. IJSRuntime is registered by the Blazor framework. NET methods from JavaScript functions in ASP.NET Core Blazor.
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