Checking if a key exists in a JavaScript object?

I do it as following

const obj = { a: 1, b: 2, c: 3 };

// Using the 'in' operator
console.log('a' in obj); // true
console.log('d' in obj); // false

// Using the 'hasOwnProperty' method
console.log(obj.hasOwnProperty('b')); // true
console.log(obj.hasOwnProperty('d')); // false

New awesome solution with JavaScript Destructuring:

let obj = {
    "key1": "value1",
    "key2": "value2",
    "key3": "value3",
};

let {key1, key2, key3, key4} = obj;

// key1 = "value1"
// key2 = "value2"
// key3 = "value3"
// key4 = undefined

// Can easily use `if` here on key4
if(!key4) { console.log("key not present"); } // Key not present

Do check other use of JavaScript Destructuring

A fast and easy solution is to convert your object to json then you will be able to do this easy task:

const allowed = {
    '/login' : '',
    '/register': '',
    '/resetpsw': ''
};
console.log('/login' in allowed); //returns true

If you use an array the object key will be converted to integers ex 0,1,2,3 etc. therefore, it will always be false