How to iterate over the keys and values in an object in CoffeeScript?
JavascriptCoffeescriptJavascript Problem Overview
I have an object (an "associate array" so to say - also known as a plain JavaScript object):
obj = {}
obj["Foo"] = "Bar"
obj["bar"] = "Foo"
I want to iterate over obj
using CoffeeScript as follows:
# CS
for elem in obj
bu the CS code above compiles to JS:
// JS
for (i = 0, len = obj.length; i < len; i++)
which isn't appropriate in this case.
The JavaScript way would be for(var key in obj)
but now I'm wondering: how can I do this in CoffeeScript?
Javascript Solutions
Solution 1 - Javascript
Use for x,y of L
. Relevant documentation.
ages = {}
ages["jim"] = 12
ages["john"] = 7
for k,v of ages
console.log k + " is " + v
Outputs
jim is 12
john is 7
You may also want to consider the variant for own k,v of ages
as mentioned by Aaron Dufour in the comments. This adds a check to exclude properties inherited from the prototype, which is probably not an issue in this example but may be if you are building on top of other stuff.
Solution 2 - Javascript
You're initializing an array, but then you're using it like an object (there is no "associative array" in js).
Use the syntax for iterating over objects (something like):
for key, val of arr
console.log key + ': ' + val
Solution 3 - Javascript
The short hand version using array comprehension, which can be used as a one-line loop.
console.log index + ": " + elm for index, elm of array
Array comprehension are:
> "Comprehensions replace (and compile into) for loops, with optional > guard clauses and the value of the current array index. Unlike for > loops, array comprehensions are expressions, and can be returned and > assigned.", http://coffeescript.org/#loops
Solution 4 - Javascript
with your convention, arr is an array, but "foo" is a property of this array, it is not an indexed value. If you want to store your data the indexed values of an array, you should have written :
arr1 = []
arr1[0] = "Bar"
arr1[1] = "Foo"
or if you want an associative array, just use an object :
arr2 = {}
arr2["Foo"] = "Bar" // equivalent to arr2.foo="Bar"
arr2["bar"] = "Foo" // equivalent to arr2.bar="Foo"
if you want to loop over arr1 :
str = "values are : "
for val in arr2
str += val + " |"
console.log key + ': ' + val
returns :
values are : Bar | Foo |
and to loop over arr2 : "for value in array"
for key, val of arr
console.log key + ': ' + val
which returns :
Foo : Bar
Bar : Foo