A litlle example code to read data from a MCP3002 on a RPi using pi-spi

mcp3002.js

'use strict';

var SPI = require('pi-spi');

var spi = SPI.initialize("/dev/spidev0.0");

// Read value from a MCP3002 (http://ww1.microchip.com/downloads/en/DeviceDoc/21294C.pdf)
function readMCP(channel, callback) {
    if (spi === undefined) return;
    var mode = (8 + channel) << 4;
    var tx = new Buffer([1, mode, 0]);
    var rx = new Buffer([0, 0, 0]);

    spi.transfer(tx, tx.length, function(err, buffer) {
        var value = ((buffer[1] & 3) << 8) + buffer[2];
        callback(value);
    });
}

setInterval(function () {
        readMCP(0, function (value) {
                console.log(value);
        });
}, 100);

Here is an example of how to connect it (example with a photoresistor)

Also, here is the datasheet