Node-RED Pricewatch

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Let Node-RED check on a daily basis the actual product prices on different websites for you and only send a notification when it meets your desired price.

Node-RED Pricewatch

How it works

With this flow it downloads a whole webpage and via HTML and CSS element names it filters out only the price of the product. Then compare the price with the desired price. If this is lower it sends a message with the product name, current price and a link to your phone as notification.

Now you only need to click on the link and order it!

Flow explanation

With this flow you can check a website for the actual price of a product.

Node-RED flow

Explanation of each node:

[inject node] Trigger this flow every day at 12.00.

Repeat     at a specific time
at         12.00 
on         (Check all the days to check)

[http request node] Download the webpage.
```
Method     GET
URL        (the full url of the webpage)
```
Output msg.payload:
```
<html><head>...<div id="price">20,95</div>...</head></html>
```
Sometimes you can try the other options if there is no data as output of this node.
[html node] This node filters away all data to only return the actual price on the page. This Selector is different on each page and the hardest part to find.
See CSS Selector how you can define your own required Selector.
```
Property   msg.payload
Selector   #price
Output     only the text content of the elements
           as a single message containing an array
           in msg.payload
```
Output msg.payload:
```
20,95
```
[change node] Extract the price to a real number (no cents are used).
```
Set           msg.payload
to the value  [expression] $number((payload.$split(',')[0]))  
```
Output msg.payload:
```
20
```
See Price formatter examples how you can convert a text to extract only the raw price.
[switch node] Compare the raw price with your desired price.
```
Property   msg.payload 
           '<=' [number] 20     
```
Is your input price smaller or equal (<=) then your desired price (for example 20) then the flow continues otherwise it stops here.

Output msg.payload:
```
20
```

[template node] Create a notification message text.

Property    msg.payload
Template    The fabric softener is on sale! Current price 
            https://www.bol.com/nl/p/robijn-puur-zacht-wasverzachter-4-x-18-wasbeurten-voordeelverpakking/9200000108581694/

Output msg.payload:

The fabric softener is on sale! Current price 20
https://www.bol.com/nl/p/robijn-puur-zacht-wasverzachter-4-x-18-wasbeurten-voordeelverpakking/9200000108581694/

[delay node] Only send a notification once per 3 days.

Action Rate Limit
       All messages
Rate  1 [msg(s) per] 3 [Days]
      Drop intermediate messages

The output msg.payload is still the same.

[debug node] Gets only the message when the product has the desired price. This node should be replaced and connected with your own configured notification app.

This is how this message looks like in Telegram.

Flows for different sites

Here I defined the Selectors and Price formatter node values for some sites. I also add an example flow for each site. In the examples, I used high prices to trigger the notification.

Amazon.com / Amazon.de

NOTE: I have problems getting the content of this page. Please let me know if you have a solution for this.

Selector:       .a-price-whole

Price formatter: $number(payload.$split('<')[0])

Amazon.nl

Selector:       #corePrice_feature_div > div > div > span.a-price.aok-align-center > span:nth-child(2) > span.a-price-whole

Price formatter: $number(payload.$split(',')[0])

Download an Amazon.nl example flow.

Bol.com

Selector:       .buy-block .promo-price

Price formatter: $number((payload.$split('\n')[0]))

Download a Bol.com example flow.

iBood.com

Selector:       ._price_n1pwc_7

Price formatter: $number((payload[0].$split(',')[0]))

Download an iBood example flow.

Kruidvat.nl

Selector:       .pricebadge__new-price-decimal

Price formatter: $number(payload[0])

Download a Kruidvat example flow

NOTE: If they change their site structure, this will break. Let me know here if one is broken then I can fix it.

Create your own prize checker

– does the page work with the http request node?

The html node use CSS4 and/or jQuery to grabs the correct CSS element. The CSS name is normally used to style the element on the page with size, color, etc.

Price Formatter examples

What you need is the raw price, without decimals, and as number. Only with this value you can compare the price if it match your desired price.

With new lines

The price is spread over multiple lines.

20
95

Convert the values by putting each value in a new array element after each new line (\n) Then only use the data in the first element ([0]) Then convert the value from a string to a number ($number())

$number((payload.$split('\n')[0]))

Other format?

Panic? If the above examples don’t match your format, Google for it to find out how you can extract the price. That’s also how I find mine! Let me know if you have some additions, then I can add those here.

Define the selector

These steps are needed to take to get the selector value to get the price:

Go to the page try.jsoup.org
Click on the button Fetch URL
Fill in the url to try
Click on the button Fetch. Now the whole page source is loaded

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