How to preload iframes?

@aniya.jaskolski 

Preloading iframes can help enhance performance and improve user experience on a website. Here are some ways to preload iframes:

1. Use the preload attribute: You can add the "preload" attribute to the iframe tag in your HTML code. This attribute tells the browser to preload the iframe content before it is displayed on the page.

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<iframe src="iframe.html" preload></iframe>

1. Load the iframe content in the background: You can use JavaScript to load the iframe content in the background before it is displayed on the page. This can be done by creating a new iframe element, setting its source, and then removing it from the DOM.

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var iframe = document.createElement('iframe');
iframe.style.display = 'none';
iframe.src = 'iframe.html';
document.body.appendChild(iframe);
iframe.onload = function() {
  document.body.removeChild(iframe);
};

1. Lazy loading: If you have multiple iframes on a page, you can lazy load them by only loading the iframe content when it is about to be displayed. This can be done by dynamically adding the iframe element to the page when it comes into view.

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var iframe = document.createElement('iframe');
iframe.src = 'iframe.html';
// Add the iframe to the page when it comes into view
window.addEventListener('scroll', function() {
  if (isElementInViewport(iframe)) {
    document.body.appendChild(iframe);
    window.removeEventListener('scroll', this);
  }
});

function isElementInViewport(el) {
  var rect = el.getBoundingClientRect();
  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
    rect.right <= (window.innerWidth || document.documentElement.clientWidth)
  );
}

By preloading iframes, you can ensure that the content is ready to be displayed when needed, leading to a smoother and faster user experience.