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Chapter 2 - Life Support

In this chapter, you will get your life support systems online by implementing some simple operations on numbers, strings and boolean values.

To do that, you will need to

  • understand function parameters,
  • know how to define and initialize variables and
  • know about operators for
    • strings,
    • numbers and
    • booleans.

Finding the source code

The JavaScript filepath for this lesson is 

src/lifeSupport.js

Go on and open it up in your editor.

Challenges

Finally, your bridge computer is online and showing you the current state of affairs. However, you really don't like what you are seeing - hardly any main system is functional!

The most immediate problem seems to be that the life support systems have gone haywire, you'll need to set up some simple routines to make sure that it doesn't get too chilly, and that the air stays clean.

To pile up on bad news, your main reactor is still offline - you'll need to look into that later. The good news is that the backup reactor is running. But that limits the subsystems that you can have online at any time, so you'll need to find a way of deciding what to turn on and what not to.

Calculate Power requirements

First things first, the calculation routine for estimating power requirements is gone. Luckily, it's a rather simple calculation.

Find the function calculatePowerRequirements. It takes three numbers as parameter, representing the energy need for lighting, heating and airflow. The function is supposed to just calculate the sum of these values and return it. The mainframe computer is going to run one calculation for each of the areas of your ship, passing in the area's requirements for lighting, heating and airflow accordingly.

Hint: Short code is not always good code. In most cases, an explicit statement of what your code is supposed to be doing helps with code readability, so how easy it is to read your solution. One way of improving readability is giving clear names to calculation steps and sums. As part of the exercise, define a constant with a fitting name inside of the calculatePowerRequirements function, and assign it the value of your calculation. Then, return that constant.

Hint Hint: Most of the JavaScript world has agreed on camelCase for variable names - that is, a lower case letter at the beginning, with an upper case letter for additional words.

Decide on subsystems to keep online

Even after fixing the power requirement calculation, there's still a bit too little juice left to get everything running smoothly. You'll need to turn off some of the non-critical life support sub systems, preferably those that have a high power draw.

To do so, update the keepSubSystemOnline function. This function takes two boolean parameters, isCriticalSystem and hasHighEnergyDraw.

The ship mainframe computer expects a boolean value, telling it whether to keep a system it describes via the two parameters online.

Fix unit of temperature control

It seems that there is a bug in the temperature control, somehow the default has been set to degrees Kelvin, but the heating systems still expect a value in degrees Celsius - that can't be good.

Luckily, you remember that the conversion was x°K = (x - 273.15)°C.

To fix the problem, implement the getTemperatureWithUnit function. It only has one parameter, temperatureInKelvin, which is numeric.

What it expects as output is a string of the form "28°C" - so a number, followed by °C.

This function will be run with multiple operating temperatures in Kelvin, if all of them return the correct string in degrees Celsius, the problem is fixed.

Testing your progress

Once all the tasks in this lesson are done, your system should display:

  Life support............................... online

and show the subsystem trace for the next main system to fix, the main reactor:

===========================================================
  Starting failed subsytem trace
  Tracing main reactor components
===========================================================

Next steps

This is the end of the introduction lesson. The next one will combine most things you have learned so far, including functions and if and if ... else statements and the Math library.