vanilla script prev from jquery prev

prev.js

/*
 * It returns previous element sibling
 *    works like jquery's `prev` but combined selector is not supported
 *
 */
var prev = function(target, selector) {
    var siblings = target.parentNode.children;
    var previousElementSibling;

    for (var i = Array.prototype.indexOf.call(siblings, target) - 1; i >= 0; i--) {
        if (selector[0] === ".") {
            if (siblings[i].classList.contains(selector.substr(1))) {
                previousElementSibling = siblings[i];
                break;
            }
        } else if (selector[0] === "#") {
            if (siblings[i].id === selector.substr(1)) {
                previousElementSibling = siblings[i];
                break;
            }
        } else {
            if (siblings[i].tagName.toLowerCase() === selector) {
                previousElementSibling = siblings[i];
                break;
            }
        }
    }

    return previousElementSibling;
};