lsm9ds1

I’m starting work on an I2C driver for the Sparkfun 9DoF Sensor Stick
https://www.sparkfun.com/products/13944
3-axis Magnetometer, Gyro and Accelerometer.
As a starting point I’ve downloaded the Arduino Library from
https://github.com/sparkfun/SparkFun_LSM9DS1_Arduino_Library
I’ve edited the LSM9DS1_register.h header file changing the #define to a variable object.

I looked at some existing modules and found an interesting comment in this one.
https://www.espruino.com/modules/ADS1X15.js
The comment:

/* Register values. Most of these aren't used
and this is hidden, so it'll get optimised out
when minified */
var CONFIG = {
OS_MASK      : (0x8000),
OS_SINGLE    : (0x8000),  // Write: Set to start a single-conversion
OS_BUSY      : (0x0000),  // Read: Bit = 0 when conversion is in progress
OS_NOTBUSY   : (0x8000),  // Read: Bit = 1 when device is not performing a conversion

What minification settings are used to make this trick work?