如何获取此数组的特定值

Question

I have this array with addresses and countries associated to each address.

So Im trying to get the createdAt value from address where the country name is USA

How can I return exactly this ('1623775723413')

[
  address {
    id: 1,
    createdAt: '1623775723413',
    updatedAt: '1623775723413',
    description: '123 W Beaver',
    country: Country {
      id: 1,
      createdAt: '1623556846082',
      updatedAt: '1623556846082',
      name: 'USA',
    }
  },
  address {
    id: 2,
    createdAt: '1623775809090',
    updatedAt: '1623775809090',
    description: '345 MH Lodge',
    country: Country {
      id: 2,
      createdAt: '1623556846082',
      updatedAt: '1623556846082',
      name: 'Germany',
    }
  },
  address {
    id: 3,
    createdAt: '1623775999999',
    updatedAt: '1623775999999',
    description: '564 Brighton',
    country: Country {
      id: 3,
      createdAt: '1623556846082',
      updatedAt: '1623556846082',
      name: 'France',
    }
  }
]

Answer 1

You have to use find method from Array prototype - it will return first matching element, or undefined if no matching elements are present:

const item = arr.find(addr => addr.country.name === 'USA');

if (item) {
  console.log(item.country.createdAt);
}

Plus as mentioned in answer above, array is in wrong format.

You can shorten solution even more by using optional chaining (it is widely supported by all modern browsers, except for internet explorer - so widely supported by all modern browsers):

console.log(arr.find(addr => addr.country.name === 'USA')?.country.createdAt);

Answer 2

You cant format arrays like that in JavaScript. So you first need to format it to look like this. The way you are writing them are like associative arrays in PHP but Javascript doesn't have that.

const items = [
  {
    id: 1,
    createdAt: '1623775723413',
    updatedAt: '1623775723413',
    description: '123 W Beaver',
    country: {
      id: 1,
      createdAt: '1623556846082',
      updatedAt: '1623556846082',
      name: 'USA',
    }
  },
  {
    id: 2,
    createdAt: '1623775809090',
    updatedAt: '1623775809090',
    description: '345 MH Lodge',
    country: {
      id: 2,
      createdAt: '1623556846082',
      updatedAt: '1623556846082',
      name: 'Germany',
    }
  },
  {
    id: 3,
    createdAt: '1623775999999',
    updatedAt: '1623775999999',
    description: '564 Brighton',
    country: {
      id: 3,
      createdAt: '1623556846082',
      updatedAt: '1623556846082',
      name: 'France',
    }
  }
]

You then need to loop over the array and find the array the object that you want.

for (let index = 0; index < items.length; index++) {
  const singleItem = items[index];
  if(items[index].country.name === 'USA'){
    console.log(items[index].createdAt)
    break;
  }
}

Edit .

The other answer would actually be a faster way to find the country so you could combine these two answers together to fully solve the question.