从对象数组获取键值

Question

I am trying to extract the names of all keys from an array of objects keeping time complexity as n(One loop only). The array is as below:

var addressArray = [{"city":"New York"},{"country":"USA"},{"zip": 45677}];

I want to extract the below:

var addressKeys = ["city", "country", "zip"].

I am able to do the same by first looping through the array and then using a key in obj loop but that doesn't loo good. Alternatives are most welcome.

Answer 1

Use Object.keys to get the keys.

if (typeof Object.keys !== "function") {
    (function() {
        Object.keys = Object_keys;
        function Object_keys(objectToGet) {
            var keys = [], name;
            for (name in objectToGet) {
                if (objectToGet.hasOwnProperty(name)) {
                    keys.push(name);
                }
            }
            return keys;
        }
    })();
}

Answer 2

From your definition addressArray is an object not an array.

You can use Object.keys() to get the keys array of an object.

var addressKeys = Object.keys(addressArray);

To support older browsers , which does not support Object.keys you can use a Polyfill

Answer 3

Use for-in loop to access each key-value pair and then push to new array: (Recommended)

for(var index in addressArray){
    addressKeys.push(index)
}

Another solution is:

var addressKeys = Object.keys(addressArray)

which is slower comparatively.

Answer 4

Note that I switched []'s with {}'s:

var addressObject = {"city":"New York", "country":"USA", "zip": 45677};

var keys = [];

for(var address in addressObject)
{
    keys.push(address);
}

console.log(keys);