In JavaScript we often use Immediately Invoked Function Expessions Show archive.org snapshot (or IIFEs) to prevent local variables from bleeding into an outside scope:
(function() {
var foo = "value"; // foo is scoped to this IIFE
})();
In Coffeescript an IIFE looks like this:
(->
foo = "value" # foo is scoped to this IIFE
)()
There is also a shorthand syntax with do:
do ->
foo = "value" # foo is scoped to this IIFE
You can also use do with arguments to capture an outside name into the IIFE's scope:
for filename in list
# in this line, `filename` is subject to crazy JS/Coffeescript scoping
do (filename) ->
# in this line `filename` is scoped to this IIFE
This makes do the best way to emulate
let
Show archive.org snapshot
in Coffeescript.
Example: When you need IIFEs
You would expect the following code to open three dialogs, saying "foo", "bar" and "baz" respectively:
alerters = [];
for i in ['foo', 'bar', 'baz']
alerters.push
-> alert(i)
for alerter in alerters
alerter()
When running the code however, you will see that the three dialogs say "baz", "baz" and "baz"! This is because they all share the same i variable.
To get the desired bahvior, use do(i) to scope i to each alert function:
alerters = [];
for i in ['foo', 'bar', 'baz']
alerters.push
do (i) -> alert(i)
for alerter in alerters
alerter()
