Coffeescript syntax issue with for statement - if-statement

Question

Using Coffeescript, I am trying to set conditionals for setting a fillColor on a graph plot for two variables; lastVisibility and curr_visibility. Something is not right with my syntax. Any suggestions
for set in datasets
line.push
data: set,
lines:
show: true
fill: true
opacity: 0.7
fillColor: if lastVisibilty == 0 & curr_visibility == 0
then "#C90E30"
else lastVisibilty == 0 & curr_visibility == 1
then "#439C32"
else lastVisibilty == 1 & curr_visibility == 0
then "#C90E30"
else
"#439C32"

Answer 1

There are lots of problems here:
You only use then when you're using a one-liner such as a = if b then c else d, if you're using the multi-line form of if then you don't use thens.
You have multiple else branches where you mean else if.
& and && are different things, & is a bit-wise operator, && is the logical conjunction you're looking for.
You need to be very careful and consistent with your indentation.
Applying those adjustments to your code you get:
for set in datasets
line.push
data: set,
lines:
show: true
fill: true
opacity: 0.7
fillColor: if lastVisibilty == 0 && curr_visibility == 0
"#C90E30"
else if lastVisibilty == 0 && curr_visibility == 1
"#439C32"
else if lastVisibilty == 1 && curr_visibility == 0
"#C90E30"
else
"#439C32"
However, the conditional logic inside your loop doesn't depend on set (i.e. is loop invariant) so you should factor that out:
fillColor = if lastVisibilty == 0 && curr_visibility == 0
"#C90E30"
else if lastVisibilty == 0 && curr_visibility == 1
"#439C32"
else if lastVisibilty == 1 && curr_visibility == 0
"#C90E30"
else
"#439C32"
for set in datasets
line.push
data: set,
lines:
show: true
fill: true
opacity: 0.7
fillColor: fillColor
Or better, push all the invariant stuff outside the loop to further clarify the code:
fillColor = if lastVisibilty == 0 && curr_visibility == 0
"#C90E30"
else if lastVisibilty == 0 && curr_visibility == 1
"#439C32"
else if lastVisibilty == 1 && curr_visibility == 0
"#C90E30"
else
"#439C32"
lines =
show: true
fill: true
opacity: 0.7
fillColor: fillColor
for set in datasets
line.push
data: set,
lines: lines
Or, since a for-loop is an expression, you could say:
fillColor = if lastVisibilty == 0 && curr_visibility == 0
"#C90E30"
else if lastVisibilty == 0 && curr_visibility == 1
"#439C32"
else if lastVisibilty == 1 && curr_visibility == 0
"#C90E30"
else
"#439C32"
lines =
show: true
fill: true
opacity: 0.7
fillColor: fillColor
line = ({ data: set, lines: line } for set in datasets)
Assuming that line is empty before your loop of course; if it isn't then you could use Array.prototype.concat:
line = line.concat({data: set, lines: line } for set in datasets)
to append the loop's data to line.