gistfile1.txt

// ==UserScript==
// @name         Amazon Add to Cart
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        *://www.amazon.in/*/dp/*
// @match        *://www.amazon.in/dp/*
// @match        *://www.amazon.in/gp/product*
// @grant        none
// ==/UserScript==
/* jshint -W097 */
'use strict';

// Your code here...

var buyNowButton = document.querySelector('#buy-now-button');

var addToCardButton = document.querySelector('#add-to-cart-button')

if (addToCardButton) {
	addToCardButton.click();
    console.log('clicking add to cart button');
} else if (buyNowButton) {
	buyNowButton.click()
    console.log('clicking buy now button');
} else {
	location.reload();
}