Question

In CoffeeScript, what is the simplest way to check if a key exists in an object?

Answer 1

key of obj

This compiles to JavaScript’s key in obj. (CoffeeScript uses of when referring to keys, and in when referring to array values: val in arr will test whether val is in arr.)

thejh’s answer is correct if you want to ignore the object’s prototype. Jimmy’s answer is correct if you want to ignore keys with a null or undefined value.