The jQuery document.ready() method and the JavaScript window.onload event are both used to execute code when the HTML document has finished loading. However, there are a few key differences between them:
Execution Time:
jQuery document.ready(): The code inside $(document).ready() is executed as soon as the DOM (Document Object Model) is ready, which means it can run before all the external resources (such as images) have finished loading.
JavaScript window.onload: The code inside the window.onload event is executed only after the entire page, including external resources, has finished loading. It waits for everything, including images, scripts, and stylesheets, to be fully loaded.
Multiple Handlers:
jQuery document.ready(): You can have multiple $(document).ready() handlers in your code, and they will all be executed when the DOM is ready. They will run in the order they were declared.
JavaScript window.onload: Only one window.onload event handler can be assigned at a time. If you assign multiple handlers, the last one assigned will overwrite any previous ones.
Simplicity:
jQuery document.ready(): The $(document).ready() method is part of the jQuery library and provides a simpler syntax for executing code when the DOM is ready. It abstracts away some of the cross-browser compatibility issues that the window.onload event may encounter.
JavaScript window.onload: The window.onload event is a native JavaScript event, and using it directly requires more verbose code compared to the jQuery method. It may also require additional checks for cross-browser compatibility.
In general, if you are already using jQuery in your project, using $(document).ready() is a convenient way to ensure your code runs when the DOM is ready. However, if you're working with plain JavaScript or have specific requirements for waiting until all external resources are loaded, using the window.onload event is a better choice.