Wait for an element in the DOM

arrive.js

    /*
     * arrive.js
     * v2.4.1
     * https://github.com/uzairfarooq/arrive
     * MIT licensed
     *
     * Copyright (c) 2014-2017 Uzair Farooq
     */

    var Arrive = function (e, t, n) { "use strict"; function r(e, t, n) { l.addMethod(t, n, e.unbindEvent), l.addMethod(t, n, e.unbindEventWithSelectorOrCallback), l.addMethod(t, n, e.unbindEventWithSelectorAndCallback); } function i(e) { e.arrive = f.bindEvent, r(f, e, "unbindArrive"), e.leave = d.bindEvent, r(d, e, "unbindLeave"); } if (e.MutationObserver && "undefined" != typeof HTMLElement) { var o = 0, l = function () { var t = HTMLElement.prototype.matches || HTMLElement.prototype.webkitMatchesSelector || HTMLElement.prototype.mozMatchesSelector || HTMLElement.prototype.msMatchesSelector; return { matchesSelector: function (e, n) { return e instanceof HTMLElement && t.call(e, n); }, addMethod: function (e, t, r) { var i = e[t]; e[t] = function () { return r.length == arguments.length ? r.apply(this, arguments) : "function" == typeof i ? i.apply(this, arguments) : n; }; }, callCallbacks: function (e, t) { t && t.options.onceOnly && 1 == t.firedElems.length && (e = [e[0]]); for (var n, r = 0; n = e[r]; r++)n && n.callback && n.callback.call(n.elem, n.elem); t && t.options.onceOnly && 1 == t.firedElems.length && t.me.unbindEventWithSelectorAndCallback.call(t.target, t.selector, t.callback); }, checkChildNodesRecursively: function (e, t, n, r) { for (var i, o = 0; i = e[o]; o++)n(i, t, r) && r.push({ callback: t.callback, elem: i }), i.childNodes.length > 0 && l.checkChildNodesRecursively(i.childNodes, t, n, r); }, mergeArrays: function (e, t) { var n, r = {}; for (n in e) e.hasOwnProperty(n) && (r[n] = e[n]); for (n in t) t.hasOwnProperty(n) && (r[n] = t[n]); return r; }, toElementsArray: function (t) { return n === t || "number" == typeof t.length && t !== e || (t = [t]), t; } }; }(), c = function () { var e = function () { this._eventsBucket = [], this._beforeAdding = null, this._beforeRemoving = null; }; return e.prototype.addEvent = function (e, t, n, r) { var i = { target: e, selector: t, options: n, callback: r, firedElems: [] }; return this._beforeAdding && this._beforeAdding(i), this._eventsBucket.push(i), i; }, e.prototype.removeEvent = function (e) { for (var t, n = this._eventsBucket.length - 1; t = this._eventsBucket[n]; n--)if (e(t)) { this._beforeRemoving && this._beforeRemoving(t); var r = this._eventsBucket.splice(n, 1); r && r.length && (r[0].callback = null); } }, e.prototype.beforeAdding = function (e) { this._beforeAdding = e; }, e.prototype.beforeRemoving = function (e) { this._beforeRemoving = e; }, e; }(), a = function (t, r) { var i = new c, o = this, a = { fireOnAttributesModification: !1 }; return i.beforeAdding(function (n) { var i, l = n.target; (l === e.document || l === e) && (l = document.getElementsByTagName("html")[0]), i = new MutationObserver(function (e) { r.call(this, e, n); }); var c = t(n.options); i.observe(l, c), n.observer = i, n.me = o; }), i.beforeRemoving(function (e) { e.observer.disconnect(); }), this.bindEvent = function (e, t, n) { t = l.mergeArrays(a, t); for (var r = l.toElementsArray(this), o = 0; o < r.length; o++)i.addEvent(r[o], e, t, n); }, this.unbindEvent = function () { var e = l.toElementsArray(this); i.removeEvent(function (t) { for (var r = 0; r < e.length; r++)if (this === n || t.target === e[r]) return !0; return !1; }); }, this.unbindEventWithSelectorOrCallback = function (e) { var t, r = l.toElementsArray(this), o = e; t = "function" == typeof e ? function (e) { for (var t = 0; t < r.length; t++)if ((this === n || e.target === r[t]) && e.callback === o) return !0; return !1; } : function (t) { for (var i = 0; i < r.length; i++)if ((this === n || t.target === r[i]) && t.selector === e) return !0; return !1; }, i.removeEvent(t); }, this.unbindEventWithSelectorAndCallback = function (e, t) { var r = l.toElementsArray(this); i.removeEvent(function (i) { for (var o = 0; o < r.length; o++)if ((this === n || i.target === r[o]) && i.selector === e && i.callback === t) return !0; return !1; }); }, this; }, s = function () { function e(e) { var t = { attributes: !1, childList: !0, subtree: !0 }; return e.fireOnAttributesModification && (t.attributes = !0), t; } function t(e, t) { e.forEach(function (e) { var n = e.addedNodes, i = e.target, o = []; null !== n && n.length > 0 ? l.checkChildNodesRecursively(n, t, r, o) : "attributes" === e.type && r(i, t, o) && o.push({ callback: t.callback, elem: i }), l.callCallbacks(o, t); }); } function r(e, t) { return l.matchesSelector(e, t.selector) && (e._id === n && (e._id = o++), -1 == t.firedElems.indexOf(e._id)) ? (t.firedElems.push(e._id), !0) : !1; } var i = { fireOnAttributesModification: !1, onceOnly: !1, existing: !1 }; f = new a(e, t); var c = f.bindEvent; return f.bindEvent = function (e, t, r) { n === r ? (r = t, t = i) : t = l.mergeArrays(i, t); var o = l.toElementsArray(this); if (t.existing) { for (var a = [], s = 0; s < o.length; s++)for (var u = o[s].querySelectorAll(e), f = 0; f < u.length; f++)a.push({ callback: r, elem: u[f] }); if (t.onceOnly && a.length) return r.call(a[0].elem, a[0].elem); setTimeout(l.callCallbacks, 1, a); } c.call(this, e, t, r); }, f; }, u = function () { function e() { var e = { childList: !0, subtree: !0 }; return e; } function t(e, t) { e.forEach(function (e) { var n = e.removedNodes, i = []; null !== n && n.length > 0 && l.checkChildNodesRecursively(n, t, r, i), l.callCallbacks(i, t); }); } function r(e, t) { return l.matchesSelector(e, t.selector); } var i = {}; d = new a(e, t); var o = d.bindEvent; return d.bindEvent = function (e, t, r) { n === r ? (r = t, t = i) : t = l.mergeArrays(i, t), o.call(this, e, t, r); }, d; }, f = new s, d = new u; t && i(t.fn), i(HTMLElement.prototype), i(NodeList.prototype), i(HTMLCollection.prototype), i(HTMLDocument.prototype), i(Window.prototype); var h = {}; return r(f, h, "unbindAllArrive"), r(d, h, "unbindAllLeave"), h; } }(window, "undefined" == typeof jQuery ? null : jQuery, void 0);

waitForElm.js

function waitForElm(selector) {
    return new Promise(resolve => {
        if (document.querySelector(selector)) {
            return resolve(document.querySelector(selector));
        }

        const observer = new MutationObserver(mutations => {
            if (document.querySelector(selector)) {
                resolve(document.querySelector(selector));
                observer.disconnect();
            }
        });

        observer.observe(document.body, {
            childList: true,
            subtree: true
        });
    });
}


waitForElm('.product-description').then((elm) => {
});