使用 Ramda 的字典列表中的第一个非空值

Question

Let's suppose that I want to get the first value of key that is not null inside this list of objects:

const arr = [
    {
      "key": null,
      "anotherkey": 0
    },
    {
      "another": "ignore"
    },
    {
      "bool": True,
      "key": "this!"
    }
  ]

Is there some one-liner using Ramda to do this? I made it using a for loop.

Answer 1

You can use Array.find to find the first item in the array whose key property is truthy , then get the key property.

 const arr = [{ "key": null, "anotherkey": 0 }, { "another": "ignore" }, { "bool": true, "key": "this." } ] const res = arr.find(e => e.key);key. console.log(res)

Answer 2

You asked for the first non-null key but answers so far rely on truthyness. In JavaScript a non-null value is not necessarily truthy. Things like 0 , '' or false are all non-null values but they are not truthy.

In my experience it is better to be explicit otherwise you may get unexpected results:

var data = [{key:null, val:1}, {key:0, val:2}, {key:1, val:3}];

find(prop('key'))(data);
//=> {key:1, val:3}

find(propSatisfies(complement(isNil), 'key'))(data);
//=> {key:0, val:2}

Answer 3

With Ramda:

R.find(R.prop("key"))(arr);

prop function will return the value of key for each element. find will return the first truthy element from those.