Create new object from existing array and object

Question

I'm trying to return a new object with properties given in the existing object and keys present in a given array. I can't mutate the object and if the keys are present in the array but not in the object the key should be ignored. I get hung up on how to compare the array elements to the objects keys.

function picker(array, obj) {
    var newObj = {};
    for (var i = 0; i < arrary.length; i++) {
        if (array[i] !== obj[i]) {
            newObj[array[i]] = obj[i];
        }
    }
    return newObj;
}

var array = [
    'a',
    'c',
    'e'
];
var obj = {
    a: 1,
    b: 2,
    c: 3,
    d: 4
};

var bubble = picker(array, obj);
console.log(bubble);   result --> `{ a: 1, c: 3 }`

Answer 1

You probably meant something like this:

 function picker(array, obj) { var newObj = {}; for (var i = 0; i < array.length; i++) { if (array[i] in obj) { newObj[array[i]] = obj[array[i]]; } } return newObj; } var array = ['a', 'c', 'e']; var obj = {a: 1, b: 2, c: 3, d: 4}; console.log(picker(array, obj)); 

That is, if obj contains the property with name array[i] , then add that property to newObj .

Maybe it will be clearer if you iterate with reduce , forEach or for...of , then you won't be confused by the index i .

 function picker(array, obj) { return array.reduce(function(newObj, key) { if (key in obj) newObj[key] = obj[key]; return newObj; }, {}); } var array = ['a', 'c', 'e']; var obj = {a: 1, b: 2, c: 3, d: 4}; console.log(picker(array, obj)); 

Answer 2

You could do something like

const x = array.reduce((total, current) => current in obj ? ({
  ...total,
  [current]: obj[current]
}) : total, {});

Which basically creates an object, key after key, based only on items of the array , where the value per key is taken from obj . Check out the fiddle .

Answer 3

You haven't checked whether the key is existing in the array.

The condition if (array[i] !== obj[i]) { is trying to check the array key with object value instead of object key. Also obj[i] is incorrect, since obj[0] does not exist with the key 0 .

This is another variation using Object.keys instead of for loop.

 function picker(array, obj) { var newObj = {}; Object.keys(obj).forEach(function(key){ if(array.indexOf(key) > -1) { newObj[key] = obj[key]; } }); return newObj; } var array = ['a', 'c', 'e']; var obj = {a: 1, b: 2, c: 3, d: 4}; console.log(picker(array, obj));