Product monitor and add-to-cart-er

Monitors a product's price on Amazon and adds to cart as soon as price drops below threshhold.

Written in PhantomJS with CasperJS framework.

Installing PhantomJS and CasperJS

If you're on a Mac, it's quite simple using Homebrew.

brew install phantomjs
brew install casperjs

You may also download and install each from the websites above.

Setting up the script

There are fields at the top of the script you will need to modify.

priceThreshhold	This is the dollar amount for which the script will add the product to your cart once the price of the product falls below it.
productUrl	This is the URL to the product page on Amazon.com.
refreshInterval	This is the amount of time the script will wait before refreshing the product page when the price is still above the priceThreshhold, in milliseconds. Must be greater than zero.
scriptTimeout	This is the maximum amount of time the script will continue reloading the product page and checking the price, in milliseconds. Once this amount of time has elapsed, the script will exit. The default value is for 1 day.
loginEmail	This is the email you login with to Amazon.com.
loginPassword	This is your password.
loginName	This is the first name Amazon has stored for your account. It's the name that shows up on the top right of the page when you're signed in. It's how the script tells whether or not your already signed in, thus being able to skip the signin step.

How to run

casperjs --cookies-file=cookies.txt --disk-cache=yes casper-scrape.js

In the above command, cookies.txt can be any filename you want. It's the plain-text file PhantomJS will use to store the cookie info from signing in. When you run the script after the first time that file has been created from the script, you will already be signed in. To sign out, just delete the cookie file.

Output

When running the script the first time, you should see output like this:

Loading homepage
Checking signed-in status
Going to signin
Signing in
Signed in successfully
Loading product page (try #1 - Wed Nov 28 2012 20:08:12 GMT-0500 (EST))
Checking price
Current price: $999.99 (999.99)
Under threshhold of 800? false
Loading product page (try #2 - Wed Nov 28 2012 20:08:18 GMT-0500 (EST))
Checking price
Current price: $999.99 (999.99)
Under threshhold of 800? false

This will continue until the price of the product falls below the priceThreshhold. Once this happens, you'll see this:

Checking price
Current price: $688.00 (688.00)
Under threshhold of 800? true
Success! All systems GO!
Adding to cart
Selecting no protection coverage
Clicking edit-cart or proceed-to-checkout
Cart page
Done

In addition to all the output to your terminal above, a new directory called "images" has also been created storing the screen-captures of each of the steps run by the script. These help to debug if, for example, signing in isn't working.

Now you should be able to open your browser, sign in, and the product will be in your cart waiting for you to checkout. You will need to actually navigate to your cart to see it, as sometimes the cart item counter in the top right doesn't update until you load the cart page. But don't worry, it's there.