5 ways to check if the property exists in JavaScript Object

When I started my journey with programming, there were many problems that took time for me to understand. JavaScript Objects was one of them. However I learnt it gradually over the time after I started using it frequently. I am sure it is different topics for different people.

So today, I would like to write about how to check if the property exists in the object since it is one of the common things we deal with frequently.

1. Using Object method hasOwnProperty()

The most common solution would be to use hasOwnProperty() which is one of the common object methods. This method returns a boolean indicating whether the object has the specified property.

var favAuthor = {
  name: 'Dan Brown',
  favBook: 'Lost Symbol',
  favCharacter: 'Robert Langdon'
}
if(favAuthor.hasOwnProperty('favCharacter')) // true
{console.log('The property exists')}
else {
  console.log('The property does not exist')
}

2. in Operator

The in operator returns true if the specified property is in the specified object.

var favAuthor = {
  name: 'Dan Brown',
  favBook: 'Lost Symbol',
  favCharacter: 'Robert Langdon'
}
if('name' in favAuthor) // true
{console.log('The property exists')}
else {
  console.log('The property does not exist')
}

3. Using typeof and compare it with undefined

If the property doesn’t exist, the type of the property should be ’undefined' and hence we can use typeof operator and comparing it with ’undefined' .

var favAuthor = {
  name: 'Dan Brown',
  favBook: 'Lost Symbol',
  favCharacter: 'Robert Langdon'
}
if(typeof favAuthor.name !== 'undefined') // true
{console.log('The property exists')}
else {
  console.log('The property does not exist')
}

4. Using !! operator (double-bang operator)

This is the least known method to check the property in the object. In JavaScript, every value has an associated boolean, true or false. For example, a null value has an associated boolean value of false. A string value, such as abc has an associated boolean value of true.

You can find the list of truthy values here and the falsy values here.

Null is a falsy value.

!!null // false

So we can take advantage of that by the name of the property we want to check using the !! operator. If the key to the property value is not null, it will return true

var favAuthor = {
  name: 'Dan Brown',
  favBook: 'Lost Symbol',
  favCharacter: 'Robert Langdon'
}
if(!!favAuthor.name) // true
{console.log('The property exists')}
else {
  console.log('The property does not exist')
}

5. Using Optical Chaining

You can return true or false by using optical chaining. It returns undefined if the property does not exist which we can take advantage of.

var favAuthor = {
  name: 'Dan Brown',
  favBook: 'Lost Symbol',
  favCharacter: 'Robert Langdon'
}
if(favAuthor?.name != undefined) {
  console.log('Property exists')
}
else {
  console.log('Property does not exist')
}

Comment below if you know any other ways.

Thank You