Explain the difference between the `DOMContentLoaded` and `load` events in JavaScript and their implications for web page performance.

The `DOMContentLoaded` and `load` events in JavaScript represent different stages in the loading process of a web page. Understanding the distinction between them is crucial for optimizing web page performance and ensuring a smooth user experience.

The `DOMContentLoaded` event is fired when the initial HTML document has been completely loaded and parsed. This means that the browser has finished reading and interpreting the HTML structure of the page, and the DOM (Document Object Model) tree is fully constructed. However, external resources such as stylesheets, images, and subframes may not have finished loading at this point. JavaScript code that relies on the DOM structure, such as manipulating elements or attaching event listeners, can safely execute when the `DOMContentLoaded` event is fired.

On the other hand, the `load` event is fired when the entire page has finished loading, including all dependent resources such as stylesheets, images, scripts, and subframes. This event indicates that everything necessary for the user to interact with the page is available. JavaScript code that needs to work with these external resources, such as determining image dimensions or applying styles, should wait for the `load` event.

Here's an example to illustrate the difference:

```javascript
document.addEventListener('DOMContentLoaded', function() {
// This code will execute when the HTML document is fully parsed,
// even if images and stylesheets are still loading.
console.log('DOMContentLoaded event fired');
var element = document.getElementById('myElement');
if (element) {
element.textContent = 'Content loaded!';
}
});

window.addEventListener('load', function() {
// This code will execute when all resources, including images and stylesheets,
// have finished loading.
console.log('load event fired');
var img = document.getElementById('myImage');
if (img) {
console.log('Image dimensions:', img.width, img.height);
}
});
```

In this example, the code attached to the `DOMContentLoaded` event listener will execute as soon as the HTML document is parsed. It finds an element with the ID 'myElement' and changes its text content. This can happen before the images on the page are loaded. The code attached to the `load` event listener will wait until all resources, including the image with the ID 'myImage', have been loaded. Only then will it log the image's dimensions.

The implications for web page performance are significant. By using `DOMContentLoaded`, you can execute JavaScript code that manipulates the DOM earlier in the page loading process. This allows you to provide a faster initial user experience, as the user can start interacting with the page even before all external resources have finished loading. For example, you can display initial content, enable form interactions, or start animations.

Waiting for the `load` event is necessary for code that depends on external resources, but it can delay the execution of other JavaScript code. It's generally recommended to avoid using the `load` event unless you specifically need to work with fully loaded resources. Prioritize using `DOMContentLoaded` to improve the perceived performance of your web page. If you need to know when a specific image loads, you can attach an event listener to the image's `onload` event rather than waiting for the entire page to load.

In summary, `DOMContentLoaded` fires when the HTML is parsed and the DOM is ready, while `load` fires when all resources are loaded. Using `DOMContentLoaded` strategically allows for faster perceived performance and improved user experience by enabling JavaScript to interact with the DOM before all resources are fully loaded.