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Function Modifiers
In JavaScript, the this keyword is dynamically scoped to mean the object that the current function is attached to. If you pass a function as a callback or attach it to a different object, the original value of this will be lost. If you’re not familiar with this behavior, this Digital Web article gives a good overview of the quirks.
The fat arrow => can be used to both define a function, and to bind it to the current value of this, right on the spot. This is helpful when using callback-based libraries like Prototype or jQuery, for creating iterator functions to pass to each, or event-handler functions to use with on. Functions created with the fat arrow are able to access properties of the this where they’re defined.
codeFor('fat_arrow')
If we had used -> in the callback above, @customer would have referred to the undefined “customer” property of the DOM element, and trying to call purchase() on it would have raised an exception.
When used in a class definition, methods declared with the fat arrow will be automatically bound to each instance of the class when the instance is constructed.
CoffeeScript also supports generator functions and async functions through the yield and await keywords respectively. There's no function*(){} or async function(){} nonsense — a generator in CoffeeScript is simply a function that yields, and an async function in CoffeeScript is simply a function that awaits.
codeFor('generators', 'ps.next().value')
yield* is called yield from, and yield return may be used if you need to force a generator that doesn’t yield.
You can iterate over a generator function using for…from.
codeFor('generator_iteration', 'getFibonacciNumbers(10)')
Similar to how yield return forces a generator, await return may be used to force a function to be async.
codeFor('async', true)