How do you query objects in JavaScript?

You can use the map function of arrays, which returns another array:

const result = addresses.map(address => address.state)
console.log(result) // ['NC', 'NC', 'VA']

You can use the .map() function. Here some exemples:

var addresses = [
    { street: '104 Bob st', city: 'Boringville', state: 'NC' },
    { street: '207 Ted rd', city: 'Quiettown', state: 'NC' },
    { street: '309 Jim ln', city: 'Lameburg', state: 'VA' }
];

var states = addresses.map(a => a.state);
var cities = addresses.map(a => a.city);
var fullAddress = address.map(a => a.street + ', ' + a.city + '/' + a.state);

You just need to pass a function as parameter. The function has to produce a new value for each element that comes from the array. In my exemples, a represents each individual element of the array. Everything that comes after the arrow (=>) is what each element should produce. You can use operations, call other functions... anything really. The result is a new array that has the same length of the original array and contains the result for each element in the same order.

var addresses = [
{ street: '104 Bob st', city: 'Boringville', state: 'NC' },
{ street: '207 Ted rd', city: 'Quiettown', state: 'NC' },
{ street: '309 Jim ln', city: 'Lameburg', state: 'VA' }];


const fullAddress = addresses.map(address => {
return `State: ${address.state}, City: ${address.city}, Street:${address.street}`;
});
console.log(fullAddress);

using template string, object destructuring and implicit return, you don't need a curly bracket and return statement; A clearer way using es6

const fullAddress = addresses.map(({street, city, state}) =>
`State: ${state}, City: ${city}, Street:${street}`);
console.log(fullAddress);

or you could use the filter method.

 var addresses = [
    { street: '104 Bob st', city: 'Boringville', state: 'NC' },
    { street: '207 Ted rd', city: 'Quiettown', state: 'NC' },
    { street: '309 Jim ln', city: 'Lameburg', state: 'VA' }
    ];
    
    const result = addresses.filter(address => address.state=='NC');
    
    console.log(result);

You could mimic some SQL statments in Javascript, like

• JS: Filter array of objects by max value per category

• SQL query to get a joinned table

As an alternative, you could use a LINQ style request language, for example.

var addresses = [
        { street: '104 Bob st', city: 'Boringville', state: 'NC' },
        { street: '207 Ted rd', city: 'Quiettown', state: 'NC' },
        { street: '309 Jim ln', city: 'Lameburg', state: 'VA' }
    ],
    cities = Enumerable.From(addresses).Select('$.city').ToArray(),
    states = Enumerable.From(addresses).Select('$.state').Distinct().ToArray();
    
console.log(...cities);
console.log(...states);

<script src="https://cdnjs.cloudflare.com/ajax/libs/linq.js/2.2.0.2/linq.js"></script>