How to check if a property is undefined in JavaScript Object
Learn the proper way to check if an object property is undefined in JavaScript.
Consider we have the following object.
const obj = {
name: "king",
place: "denmark"
}
If we log for a property that is not defined in the above object, we will see an undefined
value.
console.log(obj.age); // undefined
Using typeof operator
We can use the typeof operator to check if an object property is undefined.
The typeof
operator returns the string representation of a given object property type.
if (typeof obj.age === 'undefined'){
console.log('age property is undefined');
}
Using in operator
Similary, we can also use the in
operator to check the object property existence.
The in
operator returns true if a property is present in the object, else it returns false.
const obj = {
name: "king",
place: "denmark"
}
if ('age' in obj){
console.log('age property is defined');
} else{
console.log('age property is undefined');
}