The Coffeescript Keyword Nobody's Heard Of: 'by'

Coffeescript is an amazing language. As a matter of fact, it’s one of my favorite languages, second only to JavaScript. Here’s some recent code I used to split up one array into a multidimensional array with a certain number of columns.

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matrix.push arr[i..(i + cols - 1)] for i in [0..arr.length - 1] by cols

Notice the second to last keyword: by.

The by keyword basically changes the increment of the generated for loop. Without the by, you’d have i++ as the increment of your for loop. However, with the by, you’d instead have i += 3 if you had by 3.

Here’s a simple example where I am getting money out of my bank account in the form of 5 dollar bills.

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console.log "I have #{i} dollars." for i in [0..100] by 5

This translates to the following Javascript:

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var i;
for (i = 0; i <= 100; i += 5) {
  console.log("I have " + i + " dollars.");
}

As you can see, the increment of the loop is now 5 rather than just 1.

Now the question is, are there any other hidden features of Coffeescript like this?