How to find the nearest common ancestors of two or more nodes?

Question

Users selects two or more elements in a HTML page. What i want to accomplish is to find those elements\' common ancestors (so body node would be the common ancestor if none

Answer 1

Somewhat late to the party, here's a JavaScript ES6 version that uses Array.prototype.reduce() and Node.contains(), and can take any number of elements as parameters:

function closestCommonAncestor(...elements) {
    const reducer = (prev, current) => current.parentElement.contains(prev) ? current.parentElement : prev;
    return elements.reduce(reducer, elements[0]);
}

const element1 = document.getElementById('element1');
const element2 = document.getElementById('element2');
const commonAncestor = closestCommonAncestor(element1, element2);