Comprehensions

In a lot of our iterating examples, we’ve had very simple code blocks we wanted to execute, like this one:

Example: (source: iterating_arrays.coffee)

---

myLetters = ["a", "b", "c", "d"]

for letter in myLetters
  console.log letter.toUpperCase()

---

Because we are using a single line code block with our for loop, we are able to take advantage of what CoffeeScript calls comprehensions. Comprehensions are, essentially, loops and their code blocks on the same line.

Here’s what that same example would look like using comprehensions:

Example: (source: iterating_arrays_comprehension.coffee)

---

myLetters = ["a", "b", "c", "d"]

console.log letter.toUpperCase() for letter in myLetters

---

Example: (source: iterating_arrays_comprehension.js)

---

(function() {
  var letter, myLetters, _i, _len;

  myLetters = ["a", "b", "c", "d"];

  for (_i = 0, _len = myLetters.length; _i < _len; _i++) {
    letter = myLetters[_i];
    console.log(letter.toUpperCase());
  }

}).call(this);