Why doesn't this work?

Hello all, I have a seemingly quick question. I am playing around with arrays and have come across a problem when trying to append under a conditional statement. 

I'm not sure why my code works with the boolean in the precondition but doesn't when I take it out and try to use the (definition.selection == selection.K) if fails....???? 

FeatureScript 686;
import(path : "onshape/std/geometry.fs", version : "686.0");

export enum selection
{
    annotation { "Name" : "1" }
    A,
    annotation { "Name" : "2" }
    B,
    annotation { "Name" : "3" }
    C,
    annotation { "Name" : "4" }
    D,
    annotation { "Name" : "5" }
    E,
    annotation { "Name" : "6" }
    F,
    annotation { "Name" : "7" }
    G,
    annotation { "Name" : "8" }
    H,
    annotation { "Name" : "9" }
    I,
    annotation { "Name" : "10" }
    J,
    annotation { "Name" : "Custom" }
    K
}

function selectionID(value is selection)
{
    return {
                "A" : 0,
                "B" : 1,
                "C" : 2,
                "D" : 3,
                "E" : 4,
                "F" : 5,
                "G" : 6,
                "H" : 7,
                "I" : 8,
                "J" : 9,
                "K" : 10
            }[value as string];

}

annotation { "Feature Type Name" : "My Feature" }
export const myFeature = defineFeature(function(context is Context, id is Id, definition is map)
    precondition
    {
        annotation { "Name" : "Selection" }
        definition.selection is selection;

        if (definition.selection == selection.K)
        {
            annotation { "Name" : "My Count" }
            isInteger(definition.myCount, POSITIVE_COUNT_BOUNDS);
            
            annotation { "Name" : "My Boolean" }
            definition.myBoolean is boolean;   
        }
    }
    {

        var selection = selectionID(definition.selection);
        var myArray = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100];

        // if (definition.selection == selection.K)
        if(definition.myBoolean)
        {
            myArray = append(myArray, definition.myCount);

        }
        var sketch1 = newSketch(context, id + "sketch1", {
                "sketchPlane" : qCreatedBy(makeId("Front"), EntityType.FACE)
            });
        skLineSegment(sketch1, "line1", {
                    "start" : vector(0, 0) * inch,
                    "end" : vector(0, myArray[selection]) * inch
                });
        skSolve(sketch1);
    });