How Can I Implement Callbacks to Handle Image Load Events in JavaScript?

Implement Callbacks for Image Load Events

When working with images in web applications, knowing when they have finished loading becomes crucial for certain functionalities. An efficient way to achieve this is through the use of callbacks. In this article, we'll explore how to run a JavaScript callback as soon as an image finishes loading.

Using .complete with Callbacks

For a standards-compliant method without additional dependencies, you can utilize the .complete property along with callback functions. This technique ensures that you don't wait longer than necessary for the image to load:

var img = document.querySelector('img');

function loaded() {
  alert('loaded');
}

if (img.complete) {
  loaded();
} else {
  img.addEventListener('load', loaded);
  img.addEventListener('error', function() {
    alert('error');
  });
}

This code snippet first checks if the image is already loaded by examining its .complete property. If it's true, the loaded() callback is invoked immediately. If it's false, event listeners are attached to the load and error events to handle the callback and error handling, respectively.

This method is reliable and ensures that the callback is executed as soon as the image is fully loaded, minimizing unnecessary waiting time.

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