CODEWITHSUNDEEP
javascriptcoffeescript
gsklee
gsklee

Reputation: 4934

CoffeeScript - What does this strange "Return" occurrence mean?

Consider the following CoffeeScript:

$ ->
  if localStorage["Flag1"] isnt "Done"
    localStorage["Flag1"] = "Done" # Flagged on first page loading
  $(".start").click ->
    if localStorage["Flag2"] isnt "Done"
      localStorage["Flag2"] = "Done" # Flagged on first click interaction

Which compiles into:

$(function() {
  if (localStorage["Flag1"] !== "Done") {
    localStorage["Flag1"] = "Done";
  }
  return $(".start").click(function() {
    if (localStorage["Flag2"] !== "Done") {
      return localStorage["Flag2"] = "Done";
    }
  });
});

There are two strange occurrence of "return" being planted into the rendered JavaScript. What do they do, and how will they affect the running of the script? Thanks!

Upvotes: 1

Views: 142

Answers (1)

James Allardice
James Allardice

Reputation: 165951

They won't affect the running of your script. The first return will return $(".start") (since the jQuery click method returns an instance of jQuery) from the DOM ready event handler. Since it's a callback that runs at a certain point, you can't really do anything with that return value.

The second return will return "Done", after setting the localStorage property, but again, since it's returning from a callback (a click event handler this time) you won't be able to do anything with the returned value.

I believe CoffeeScript will return the value of the last expression in each function, which is why you see those return statements in the output. From the docs:

Even though functions will always return their final value, it's both possible and encouraged to return early from a function body writing out the explicit return (return value), when you know that you're done.

Upvotes: 2

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