如何从以咖啡脚本中的值列表作为对象的地图访问第一个键

Question

I am accessing this yaml file (converted to json) using a rest call.

A:
  B:
    C: [ value1, value2, value3 ]
    D: [ value4, value5, value6 ]

looking at the json object on the uri, I see it being displayed like

{"C":["value1","value2","value3"],"D":["value4","value5","value6"]}

This result is expected, the way I am traversing the yaml file and sending it.

However, when I try to access the first key "C" of the map (yamlmap) using coffee script:

alphabet= (key for key,value of yamlmap)

It is not displaying anything. Is this the right way ?

Answer 1

As @mu-is-too-short have commented, your code is 'almost' right. But I'd recommend below.

alphabet = Object.keys yamlmap

Furthermore explanation would be easily understandable by trying web compiler on http://coffeescript.org and comparing result of it.

In short,

alphabet = (key for key of yamlmap)

which would be better than your code (key for key,value of yamlmap) which is getting-and-ignoring value of the object, is still going to be equivalent in js this big below

alphabet = (function(){
  var results = [];
  for (key in yamlmap)
    results.push(key)
  return results;
})();

While the code I recommend would be almost the same in js like below and about 2 to 3 times faster than above.

alphabet = Object.keys(yamlmap);

Many template languages can have this kind of problem and we should be aware on that.