Use Object.keys() -

let data = [{"facebook":"https://facebook.com"}, {"instagram":"https://instagram.com"}]

data.forEach(social => console.log(Object.keys(social)[0]));

Here, I'm using .forEach() instead of .map() just to log the key's name, but the idea is the same with .map().

This can be little messy and not failure proof depending on what you have in your listObj or scheduleObj. E.g. repeated date in scheduleObj can lead to a problem using this method, you may have to use another key if the dates are no unique in both lists.

scheduleObj.map((s) => {
  // get the first key of the object as the date you're going to group with
  const date = Object.keys(s)[0];

  // filter the object that matches the date
  const listObjFilter = listObj.filter((o) => Object.keys(o)[0] === date);

  // get the list for the given date (or empty array if nothing found)
  const listForDate = listObjFilter.length ? listObjFilter[0][date] : [];

  // build the result object
  return {
    [date]: {
      type: s[date]['type'],
      list: listForDate
    }
  };
})

Note that I'm always considering you have only one key in the objects inside the lists in listObj or scheduleObj.

var json = [{ _id: 123, message: 'hello', username: '1' }, { _id: 456, message: 'world', username: '2'}];
var arr = [];
for(i=0;i<json.length;i++) {
	arr.push(json[i].message);
}
console.log(arr);

There is no native map to the Object object, but how about this:

var myObject = { 'a': 1, 'b': 2, 'c': 3 };

Object.keys(myObject).forEach(function(key, index) {
  myObject[key] *= 2;
});

console.log(myObject);
// => { 'a': 2, 'b': 4, 'c': 6 }

But you could easily iterate over an object using for ... in:

var myObject = { 'a': 1, 'b': 2, 'c': 3 };

for (var key in myObject) {
  if (myObject.hasOwnProperty(key)) {
    myObject[key] *= 2;
  }
}

console.log(myObject);
// { 'a': 2, 'b': 4, 'c': 6 }

Update

A lot of people are mentioning that the previous methods do not return a new object, but rather operate on the object itself. For that matter I wanted to add another solution that returns a new object and leaves the original object as it is:

var myObject = { 'a': 1, 'b': 2, 'c': 3 };

// returns a new object with the values at each key mapped using mapFn(value)
function objectMap(object, mapFn) {
  return Object.keys(object).reduce(function(result, key) {
    result[key] = mapFn(object[key])
    return result
  }, {})
}

var newObject = objectMap(myObject, function(value) {
  return value * 2
})

console.log(newObject);
// => { 'a': 2, 'b': 4, 'c': 6 }

console.log(myObject);
// => { 'a': 1, 'b': 2, 'c': 3 }

Array.prototype.reduce reduces an array to a single value by somewhat merging the previous value with the current. The chain is initialized by an empty object {}. On every iteration a new key of myObject is added with twice the key as the value.

Update

With new ES6 features, there is a more elegant way to express objectMap.

const objectMap = (obj, fn) =>
  Object.fromEntries(
    Object.entries(obj).map(
      ([k, v], i) => [k, fn(v, k, i)]
    )
  )
  
const myObject = { a: 1, b: 2, c: 3 }

console.log(objectMap(myObject, v => 2 * v)) 

You just need to wrap object in ()

var arr = [{
  id: 1,
  name: 'bill'
}, {
  id: 2,
  name: 'ted'
}]

var result = arr.map(person => ({ value: person.id, text: person.name }));
console.log(result)

You could take the first key of the objects.

myArr1.map((key, value) => Object.keys(key)[0]);

function getData() {
    const result = Object
            .keys(myJSON.countries)
            .map(k => myJSON.countries[k])
            .map(({ currencies }) => currencies)
            .map(currency => Object.keys(currency)[0]);

    console.log(result);
}

var myJSON = { countryCode: { Australia: "AU", "United States": "US", Britain: "GB", Japan: "JP", India: "IND", France: "FR", Russia: "RS" }, countries: { AE: { currencies: { AED: { isDefault: true } } }, AL: { currencies: { ALL: { isDefault: true } } }, AU: { currencies: { AUD: { isDefault: true } } }, US: { currencies: { USD: { isDefault: true } } }, GB: { currencies: { EUR: { isDefault: true } } }, FR: { currencies: { EUR: { isDefault: true } } }, JP: { currencies: { JPY: { isDefault: true } } }, RS: { currencies: { RSD: { isDefault: false } } }, ZA: { currencies: { ZAR: { isDefault: true } } } } };
	

<button onclick="getData()">Get Data</button>

Or just in a single step:

function getData() {
    const result = Object
            .keys(myJSON.countries)
            .map(k => Object.keys(myJSON.countries[k].currencies)[0]);

    console.log(result);
}

var myJSON = { countryCode: { Australia: "AU", "United States": "US", Britain: "GB", Japan: "JP", India: "IND", France: "FR", Russia: "RS" }, countries: { AE: { currencies: { AED: { isDefault: true } } }, AL: { currencies: { ALL: { isDefault: true } } }, AU: { currencies: { AUD: { isDefault: true } } }, US: { currencies: { USD: { isDefault: true } } }, GB: { currencies: { EUR: { isDefault: true } } }, FR: { currencies: { EUR: { isDefault: true } } }, JP: { currencies: { JPY: { isDefault: true } } }, RS: { currencies: { RSD: { isDefault: false } } }, ZA: { currencies: { ZAR: { isDefault: true } } } } };
	

<button onclick="getData()">Get Data</button>

Using Object#keys and Array#forEach:

const 
  myObj = {
    prop1: 'prop1_value',
    prop2: 'prop2_value',
    subObj: { subProp1: 'subProp1_value', subProp2: 'subProp2_value', subProp3: 'subProp3_value', subprop4: 'subProp4_value' }
  },
  myArr = [ 'arrayVal_1', 'arrayVal_2', 'arrayVal_3', 'arrayVal_4' ];
  
const { subObj } = myObj;
Object.keys(subObj).forEach((prop, index) => { subObj[prop] = myArr[index] });

console.log(myObj);