According to the Grove Finger-Clip Wiki, the heart rate sensor can be interfaced with I2C and UART. You can interface it with I2C if you connect it such as shown in the “Hardware Installation” here http://www.seeedstudio.com/wiki/Grove_-_Finger-clip_Heart_Rate_Sensor .
After the hardware installation part is complete you can start with the software part. I couldn’t find any sample codes to use this sensor with node.js. However in the Wiki website I mentioned earlier there are sample codes of Arduino and Mbed. You can use this code to see what it takes to get the sensor working and make your own code that works with node.js. As another option you can use the Arduino IDE and use the code from the Wiki website to see if you get positive results.