Can someone explain this code?

Question

function _keys(obj)
{
if (!isObject(obj)) return [];
if (Object.keys) return Object.keys(obj);
var keys = [];
for (var key in obj) if (_.has(obj, key)) keys.push(key);
return keys;
}
function isObject(obj)
{
var type = typeof obj;
return type === 'function' || type === 'object' && !!obj;
}
console.log(_keys({red: "#FF0000", green: "#00FF00", white: "#FFFFFF"}));
//output
["red","green","white"]

I don't understand what this '!!' operator means. Also what's the use of 'Object.keys' and '_.has(obj, key))?
I am beginner in JavaScript programming and object. Thank you.

Answer 1

! is the logical not as Leandro Blandi said:
https://www.sololearn.com/learn/JavaScript/1133/
!! Is used to convert a value to boolean type.
Examples:
(!!false) === false
(!!true) === true
(!!42) === true
(!!0) === false
(!!undefined) === false

In your code:
type === 'object' && !!obj;
That line means: "obj is of type object and it's a truthy value"
The only 'falsey' value of type object is null so it could have been written this way:
type === 'object' && obj !== null;

Object.keys is a function that return the keys of an object:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

There's nothing called _.has() in Javascript. That's likely a utility function defined somewhere else.

A possible implementation of that function:
Edited:
function has(obj,key) {
return obj.hasOwnProperty(key);
}

Answer 2

I understand better now. Thank you.

Answer 3

The ! sign means NOT, an example:
let number = False
if (!number) {
// code goes if number is False
}
That sign is used to evaluate if a var is true or false, as I understand.