Delete Every other element

DeleteOtherElements.js

// Get an existing child element that is not the passed in element
function getFirstChildThatIsNot(parent, child) {
    return parent.children[0] != child ? parent.children[0] : parent.children[1];
}

// Get the parent node and delete everything except the passed in element
function deleteSiblingsOf(element) {
    var parent = element.parentNode;
    
    while (getFirstChildThatIsNot(parent, element)) {
        parent.removeChild(getFirstChildThatIsNot(parent, element));
    }
}

// Bottom Up recursive removal of DOM elements except for the passed in element
function removeEverythingBut(element) {
    if (!element) {
        throw new ReferenceError("HTMLElement does not exist");
    }
    
    deleteSiblingsOf(element);
    
    if (element.parentNode.tagName != 'HTML') {
        removeEverythingBut(element.parentNode);
    }
}


////////////// Test it out with different sites //////////////

// Remove everything but the Hulu Flash Video. There's more than one embed tag on hulu's main page
removeEverythingBut(document.querySelectorAll('embed')[1]);

// Remove everything but the youtube flash Video
removeEverythingBut(document.querySelector('embed'));

// Remove everything but the youtube HTML5 Video
removeEverythingBut(document.querySelector('video'));

That's nice.. How do you inject this javascript with in the page?. I am referring to an external website

@mavalur I use the javascript console. In Chrome, I just add it as a snippet and then execute it on some DOM element.