create new object from array javascript

I suggest to use a Array#forEach() and iterate over the given keys for the new object.

var obj = { name: 'Allen', last: 'Jones', age: 24, city: 'London' },
    array = ['name', 'age', 'city'],
    obj2 = {};

array.forEach(function (a) {
    obj2[a] = obj[a];
});

document.write('<pre>' + JSON.stringify(obj2, 0, 4) + '</pre>');

try this simple loop

var obj = {
    name : 'Allen',
    last : 'Jones',
    age : 24,
    city : 'London'
};
var obj2 = {};
var arr = ['name','age','city'];
arr.forEach(function(val){
   obj2[val] = obj[val]; 
});

now obj2 should have only selected properties

You may use a loop to iterate through each property. There are many approaches for that, such as for loops, while loops or foreach loops. Here's one, using a simple for loop:

var obj = {
  name: 'Allen',
  last: 'Jones',
  age: 24,
  city: 'London'
};

var arr = ['name', 'age', 'city'];
var obj2 = {};

for (var i = 0; i < arr.length; i++) {
  var property = arr[i];
  obj2[property] = obj[property];
}

Live example can be seen here.

You can delete 'last' property from existing object and the object will be same as you want.

 var obj = {
              name : 'Allen',
              last : 'Jones',
              age : 24,
              city : 'London'
           }

 delete obj.last;

 console.log(obj);

Hope this help.

Below is a general purpose method with your desired output:

var obj = {
    name : 'Allen',
    last : 'Jones',
    age : 24,
    city : 'London'
};

obj2 = ['name', 'age', 'city'];

function createObject(obj, arr) {
    var newObj = {};
  
    arr.forEach(function(value) {
        if(obj.hasOwnProperty(value)) {
            newObj[value] = obj[value];
        }
    });
  
    return newObj;
}

document.write(JSON.stringify(createObject(obj, obj2)));

There are many nice ways shown under this answer. This is a functional chainable method.

var obj = {
           name : 'Allen',
           last : 'Jones',
            age : 24,
           city : 'London'
          },
    arr = ['name', 'age', 'city'],
    res = arr.reduce((p,c) => {p[c] = obj[c]; return p} ,{});

document.write("<pre>" + JSON.stringify(res) + "</pre>");