Ways to check for an object property

ways.to.check.properties.on.objects.js

"use strict";


// There are three ways to check if an object has a property:

const obj = {
	one: 1
};

const otherObj = Object.create(obj);

// 1. !! (bang-bang)
// DON'T USE IT, it coerces your value and can give false negatives

!!obj['one']; // true
!!obj['two']; // false
!!otherObj['one']; // true
!!otherObj['two']; // false
// So far so good, but...
obj.one = false;
!!obj['one']; // false

// 2. hasOwnProperty method
// This is the recommended way

obj.hasOwnProperty('one'); // true
obj.hasOwnProperty('two'); // false

// But hasOwnProperty, as its name indicates, doesn't check the prototype chain
otherObj.hasOwnProperty('one'); // false

// 3. Using `in`
('one' in obj); // true
('two' in obj); // false
('one' in other); // true