I am trying to understand how CoffeeScript variables are scoped. According to the documentation:
This behavior is effectively identical to Ruby's scope for local variables.
However, I found out that it works differently.
In CoffeeScript
a = 1
changeValue = -> a = 3
changeValue()
console.log "a: #{a}" #This displays 3
In Ruby
a = 1
def f
a = 3
end
puts a #This displays 1
Can somebody explain it, please?
Ruby's local variables (starting with [a-z_]) are really local to the block they are declared in. So the Ruby behavior you posted is normal.
In your Coffee example, you have a closure referencing a. It's not a function declaration.
In your Ruby example, you don't have a closure but a function declaration. This is different. The Ruby equivalent to your Coffee is:
a = 1
changeValue = lambda do
a = 3
end
changeValue()
In closures, local variables present when the block is declared are still accessible when the block is executed. This is (one of the) powers of closures!
The a variable being used inside the changeValue function is the global a variable. That CoffeeScript will be compiled into the following JavaScript:
var a, changeValue;
a = 1;
changeValue = function() {
return a = 3;
};
changeValue();
console.log("a: " + a);
In order for changeValue to not alter the a variable (i.e. use a local variable), you would either need to have an argument to the function named a (which would create a as a variable local to that function) or declare a as a local variable inside the function using var a = 3; (not sure what the CoffeeScript for that would be, I'm not a CoffeeScript guy).
