Return unique selector of the element

get_unique_selector.js

/*globals document*/

var element = document.querySelector('a');

function positionInNodeList(element, nodeList) {
    for (var i = 0; i < nodeList.length; i++) {
        if (element === nodeList[i]) {
            return i;
        }
    }
    return - 1;
}

function getUniqueSelector(element) {
    var tagName = element.localName,
        selector, index, matches;
    // document.querySelectorAll("#id") returns multiple if elements share an ID
    if (element.id && document.querySelectorAll('#' + element.id).length === 1) {
        return '#' + element.id;
    }
    // Inherently unique by tag name
  
    if (tagName === 'html') {
        return 'html';
    }
    if (tagName === 'head') {
        return 'head';
    }
    if (tagName === 'body') {
        return 'body';
    }

    // We might be able to find a unique class name
    if (element.classList.length > 0) {
        for (var i = 0; i < element.classList.length; i++) {
            // Is this className unique by itself?
            selector = '.' + element.classList.item(i);
            matches = document.querySelectorAll(selector);
            if (matches.length === 1) {
                return selector;
            }
            // Maybe it's unique with a tag name?
      
            selector = tagName + selector;
            matches = document.querySelectorAll(selector);
            if (matches.length === 1) {
                return selector;
            }
            // Maybe it's unique using a tag name and nth-child
      
            index = positionInNodeList(element, element.parentNode.children) + 1;
            selector = selector + ':nth-child(' + index + ')';
            matches = document.querySelectorAll(selector);
            if (matches.length === 1) {
                return selector;
            }
        }
    }
    // Not unique enough yet.  As long as it's not a child of the document,
    // continue recursing up until it is unique enough.
  
    if (element.parentNode !== document) {
        index = positionInNodeList(element, element.parentNode.children) + 1;
        selector = getUniqueSelector(element.parentNode) + ' > ' +
        tagName + ':nth-child(' + index + ')';
    }
    return selector;
}

console.log(getUniqueSelector(element));