Pick values of given properties from object into array

Question

I have an object:

person = { 
    birth_year: 1970, 
    first_name: "John", 
    last_name: "Doe", 
    occupation: "Doctor", 
    city: "Boston",
    married: true 
}

I have an array of key names in given order:

keys = ["occupation", "last_name", "city"]

I want to get this array:

["Doctor", "Doe", "Boston"]

It is important, that the answer should guarantee the order (JavaScript does not guarantee the order for object iteration).

I think there is probably some utility function in lodash/underscore to do it simply, but can't figure out any.

Answer 1

You can use Array.prototype.map for this. Map loops through an array and creates a new array by applying a function to each item. When you use the keys array as a starting point, and return the value in o for that key, you'll get a new array with only values.

When using "dynamic" key names, you use a object[stringKeyName] notation to retrieve a value.

var o = { 
    birth_year: 1970, 
    first_name: "John", 
    last_name: "Doe", 
    occupation: "Doctor", 
    city: "Boston",
    married: true 
};

var keys = ["occupation", "last_name", "city"];

var result = keys.map(function(k) { return o[k]; });

console.log(result);

If it fits your style, you can create a helper method to replace the anonymous function:

var o = { birth_year: 1970, first_name: "John", last_name: "Doe", occupation: "Doctor", city: "Boston", married: true };
var keys = ["occupation", "last_name", "city"];

var prop = obj => key => obj[key];
var result = keys.map(prop(o));

console.log(result);