Get key value irrespective of depth in array of object

Question

I have an array of objects in which I want to get the value of a key for e.g. 'variable'. But the depth of the key is varying, like it could be as follows -

[{
    "test": {
        "nameObj": {
            "name": "DateExpires",
            "title": "DateExpires",
            "variable": "DateTime"
        },
    }
}, 
{
    "test": {
        "nameObjSomethingElse": {
            "name": "DateExpires",
            "title": "DateExpires",
            "variable": "DateTime"
        },
    }
}, 
{
    "test": {
        "nameObjSomethingElse": {
            "name": "DateExpires",
            "title": "DateExpires",
           "anotherLevel": {
            "variable": "DateTime"
           }
        }
    }
}]

In each object in the array key 'variable' is at different level and under different key. How can I get the value of 'variable'?

As I see there's more than one attribute named variable, when fetching it do you want to get them all or the first occurrence for example ? — ThS
– ThS, Commented Jul 25, 2019 at 10:59

CertainPerformance · Accepted Answer · 2019-07-25 10:59:26Z

You could use JSON.stringify and use its callback function to identify every value of a particular key:

const obj = [{
    "test": {
        "nameObj": {
            "name": "DateExpires",
            "title": "DateExpires",
            "variable": "DateTime"
        },
    }
}, 
{
    "test": {
        "nameObjSomethingElse": {
            "name": "DateExpires",
            "title": "DateExpires",
            "variable": "DateTime"
        },
    }
}, 
{
    "test": {
        "nameObjSomethingElse": {
            "name": "DateExpires",
            "title": "DateExpires",
           "anotherLevel": {
            "variable": "DateTime"
           }
        }
    }
}];
const variables = [];
JSON.stringify(obj, (key, val) => {
  if (key === 'variable') {
    variables.push(val);
  }
  return val;
});
console.log(variables);

Or, if you wanted to recurse more manually:

const obj = [{
    "test": {
        "nameObj": {
            "name": "DateExpires",
            "title": "DateExpires",
            "variable": "DateTime"
        },
    }
}, 
{
    "test": {
        "nameObjSomethingElse": {
            "name": "DateExpires",
            "title": "DateExpires",
            "variable": "DateTime"
        },
    }
}, 
{
    "test": {
        "nameObjSomethingElse": {
            "name": "DateExpires",
            "title": "DateExpires",
           "anotherLevel": {
            "variable": "DateTime"
           }
        }
    }
}];
const recurse = (obj, arr=[]) => {
  Object.entries(obj).forEach(([key, val]) => {
    if (key === 'variable') {
      arr.push(val);
    }
    if (typeof val === 'object') {
      recurse(val, arr);
    }
  });
  return arr;
};
console.log(
  recurse(obj)
);

Unless one of the values is a function with a property 'variable', or some other object that JSON.stringify can't stringify. ;-)

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