User script for checking available inventory on a Newegg product search

newegg_inventory_checker.js

// ==UserScript==
// @name         Newegg Inventory Check
// @version      5
// @description  Repeatedly refresh a given Newegg page, look for products in stock, and make a lot of noise on success
// @namespace    https://gist.github.com/damien5314/4cd478ebdbac3dc51e40c66bb884fece
// @author       https://github.com/damien5314 (forked from github.com/beporter)
// @match        https://www.newegg.com/p/*
// @match        https://secure.newegg.com/wishlist/md/*
// @grant        none
// @run-at       document-idle
// @require      https://cdnjs.cloudflare.com/ajax/libs/howler/2.1.3/howler.min.js#sha256-/Q4ZPy6sMbk627wHxuaWSIXS1y7D2KnMhsm/+od7ptE=
// ==/UserScript==
(function() {
  'use strict';

  const scanDelay = 2;
  const refreshDelay = 30;

  var readySound = new window.Howl({
    src: ['//freesound.org/data/previews/187/187404_635158-lq.mp3'],
    autoplay: false,
    loop: false,
    volume: 1.0,
  });

  function scan() {
    const results = document.evaluate(
      "//div[@class='item-container']",
      document,
      null,
      XPathResult.ANY_TYPE,
      null
    );

    var found = false;

    var itemContainer = results.iterateNext();
    while (itemContainer != null) {
      var foundMatch = false;
      if (!scanForElement(".//p[contains(., 'OUT OF STOCK')]", itemContainer) &&
        !scanForElement(".//span[contains(., 'OUT OF STOCK')]", itemContainer) &&
        !scanForElement(".//button[contains(., 'AUTO NOTIFY')]", itemContainer) &&
        !scanForElement(".//span[contains(., 'SOLD OUT')]", itemContainer)
      ) {
        console.log(`[Newegg Inventory Check] Found an item container WITHOUT an out of stock notice`);
        return itemContainer;
      }
      itemContainer = results.iterateNext();
    }

    console.log(`[Newegg Inventory Check] No products in stock`);
    return null;
  }

  function scanForElement(xpath, itemContainer) {
    var matches = document.evaluate(
      xpath,
      itemContainer,
      null,
      XPathResult.ANY_TYPE,
      null
    );
    var match = matches.iterateNext();
    return match;
  }

  function refreshInSecs(secs) {
    window.setTimeout(() => {
      window.location.reload(true);
    }, secs * 1000);
  }

  function waitToScan(callback) {
    window.setTimeout(() => {
      callback();
    }, scanDelay * 1000);
  }

  function locationStartsWithAnyOfUrls(urls) {
    return urls.reduce((acc, url) => {
      return acc || window.location.href.startsWith(url);
    }, false);
  }
  
  function tryClickAddToCart(itemContainer) {
    const button = scanForElement(".//button[contains(., 'ADD TO CART')]", itemContainer);
    if (button == null) {
      console.log(`Product found, but not "Add to Cart" present; itemContainer=`);
      console.log(itemContainer);
      return;
    }
    var clickEvent = document.createEvent('MouseEvents');
    clickEvent.initEvent('click', true, true);
    button.dispatchEvent(clickEvent);
    console.log(`Clicked "Add to Cart" for product`);
  }

  // function main()
  waitToScan(() => {
    var found = scan()
    if (found != null) {
      readySound.play();
      tryClickAddToCart(found);
    } else {
      refreshInSecs(refreshDelay);
    }
  });

})();