Gets the first value associated to an object's property

getValueByKey.js

/**
 * Gets the first value associated to an object's property.
 * Can go recursively through objects and arrays.
 *
 * @param  {Object | Array}  obj: the object or array to look for the property/index value
 * @param  {String | Number} key: the object's property name or array index
 * @return {Any}
 */
function getValueByKey(obj, key) {
  let value;
  for (const prop in obj) {
    if (prop == key) return obj[prop];
    if (obj[prop] instanceof Object) {
      value = getValueByKey(obj[prop], key);
      if (value !== undefined) return value;
    }
  }
}

test.js

var obj = {
  a: "value:a",
  b: {"inner-b": "coco"},
  c: {"inner-c": "liso", data: {"#text": "test", depth: 3}},
  d: "value:d",
};

obj.P = [
  {b: {data: {values: {":clientId": 501}}}},
  {b: {data: {values: {":clientId": 777}}}}
];

getValueByKey(obj, "b"); //{"inner-b": "coco"}
getValueByKey(obj, "data"); //{"#text": "test", depth: 3}
getValueByKey(obj, "values"); //{":clientId": 501}
getValueByKey(obj, ":clientId"); //501

var list = [
  'zero',
  'one',
  'two',
  [45, 76, 23, 87, 90],
];

var index = 2;
getValueByKey(list, index); //"two"
getValueByKey(list, 3); //[...]
getValueByKey(list, 4); //90