Check if a JavaScript object has a property

Before using an object’s property in JavaScript, we need to check if it exists first. Otherwise, error or warning will be thrown instead.

There are 2 ways to detect whether a specified property exists in a specific object.

Use in operator

in operator returns true if an object or its prototype chain contains the specified property.

let car = { brand: 'Honda', model: 'City', year: 2021 };
if('brand' in car){
	alert('yes');
}

if(!('price' in car)){
	alert('there is no price property.');
}

Use hasOwnProperty method

This object.hasOwnProperty() can be used to check an object’s own keys and will only return true if key is available on object directly.

let car = { brand: 'Honda', model: 'City', year: 2021 };
if(car.hasOwnProperty('brand')){
	alert('brand exists');
}