Plz help me understand this error in expression

Question

In a linked in learning course, there was this example expression...

It wasn't really explained well... the syntax for the b variable of the array index ([1]) on the wiggle function perhaps just shows my lack of javascript (?) familiarity.. but can someone explain how this index on the scale property is being 'used' by the wiggle function?

Perhaps asking a slightly different way... why does removing the array index ([1]) from the wiggle function cause an error on the FIRST line of code?

while omitting that b= assignment statement altogether resolves the error? It seems counter intuitive for modification in the second line like above to cause an error to the first line, and I'd like to understand what is going on so if/when I encounter other errors, I have a better understanding of how the system as a whole is functioning.

ShiveringCactus · Answer

Properties in After Effects that have two values, for example scale height and scale width, use an array in expressions.

in the expression you have:

a is being set as the width value of the scale property
b is using a wiggle, based on the value, to vary the current scale values twice per second (2) by up to 50%. But as wiggle produces an array, the expression takes the second value, which corresponds to the scale height [1].
c then sets the scale width to be a and the scale height to be b.

So by removing the [1], you're setting the scale to be [a,[50,50]] which is an array too far.

Hope that makes sense

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