Pre-Requisites

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Exercise 206-1 - A Simple Average Function

Let’s create a very simple Flow and test our function!

As usual, click +New Flow
Let’s name this “Call Code 1 - Average” and give it a description
To begin, let’s assign two numbers to calculate using “Add” Card
Click the + to make a Call Code Function.
Select the Average Function (and Average for the function within it)
Set your count to “2” (you have two values)
And let’s create a very simple “Compose” card that will give us the result.

To test, set easy values of 4 and 2, then run the Flow. You should receive a response of “3” meaning that it works!

Exercise 206-2 - Calculating a Percent Difference

Let’s now work another example that typifies working with “found code”. This implies that someone else has crafted a useful JavaScript function that you want to use - and you’ll have to make changes.

Let’s calculate Percent Difference between two values. This is defined as follows:

Percentage change : 100 % times the (Fractional change )

After an internet search, a nice piece of JavaScript is herehere:

https://ourcodeworld.com/articles/read/557/how-to-calculate-a-percentage-change-increase-and-decrease-from-2-values-in-javascript

Try loading this into the code section and see what happens! Hint: You can expect errors (which we’ll fix in the next section).

Exercise 206-3 - Fixing the Percent Difference Code

We can, however, get this to work.

First, let’s start with the Comment Block. Remember, this is CRUCIAL because it outlines the values (variables) we want to pass back and forth. We need to make some changes and include a name

This isn’t changed - much - but now we also are TYPING the parameters. That is what tells our Flow what kind of variable we’re working with (JavaScript is not strongly typed).

Exercise 206-4 - Fixing the Body of the Code

Now we have to spin this to work.

Remember we have the “req” and “res” parameters to work with … so we need to change the code within the body so it will work correctly!

To summarize the work you’ll need to do (see the image following for exact details):

Change the function name (to getPercentageChange(req,res))
Extract the input parameters (Var inputs = req.body.data;)
Catch errors (Divide by Zero)
Do the math!
Return the result (res.status(200).send({pct_difference”:output”});)

Exercise 206-5 Testing and Troubleshooting

So let’s save and set up the card …

Call Code Card
Select the code I want
Configure it
Test the card

Upon execution, you should see that you have a problem here … there’s no RESULT!

So let’s switch back to the code and see what we missed … You should find that you’re missing the RETURN parameter.

Within the comments block, add the following line (omit the first bullet!):

* @return {number} pct_difference

Running it Again:

And now we see that we do get a result, however, that result is not quite in the format we want. I really want to return a value with a certain number of decimal places … (like only 1).

Consulting JavaScript documentation, I see that the .toFixed(n) option will do what I want, so let’s add this line:

var output = difference.toFixed(1);

If you re-run, this should work as designed!