Which JavaScript object can trigger the onerror event handler?

Which JavaScript object can trigger the onerror event handler?

• A. Window
• B. Image
• C. Document
• D. XMLHttpRequest

Answer: (B)

The onerror handler is commonly used to respond to failures when loading a resource. The image element is the classic case: when the browser tries to fetch the image and the load fails (for example, a 404, network error, or blocked resource), it triggers the onerror event so you can run fallback code. This makes the image object the most straightforward and typical trigger for onerror in everyday web pages, such as using an onerror attribute to swap in a placeholder image. While other objects can be involved in error handling—window has a global error handler for uncaught JavaScript errors, and XMLHttpRequest has its own onerror for network issues—the onerror event associated with an image is the standard, direct example developers use to handle resource-loading failures.

The onerror handler is commonly used to respond to failures when loading a resource. The image element is the classic case: when the browser tries to fetch the image and the load fails (for example, a 404, network error, or blocked resource), it triggers the onerror event so you can run fallback code. This makes the image object the most straightforward and typical trigger for onerror in everyday web pages, such as using an onerror attribute to swap in a placeholder image.

While other objects can be involved in error handling—window has a global error handler for uncaught JavaScript errors, and XMLHttpRequest has its own onerror for network issues—the onerror event associated with an image is the standard, direct example developers use to handle resource-loading failures.