Check if JSON Property Exists

Check if JSON property exist using JavaScript.

You need to check if a JSON property exists, before you use it. For, example,

let obj = {
  keys: [1, 2, 3],
  empInfo: {
    firstName: 'jay',
    lastName: 'raj',
    age: 10
  }
};

In the above JSON you can access firstName as

obj.empInfo.firstName

But what if empInfo doesn’t exist. You get an error. So, you need to check if empInfo exists.

Using hasOwnProperty

You can do so using hasOwnProperty.

let obj = {
  keys: [1, 2, 3],
  empInfo: {
    firstName: 'jay',
    lastName: 'raj',
    age: 10
  }
};

if(obj.hasOwnProperty('empInfo')){
	console.log('first name is ', obj.empInfo.firstName)
}
// first name is jay

Using Optional Chaining

You can use a short hand for checking if JSON property exists using optional chaining (?.)

let obj = {
  keys: [1, 2, 3],
  empInfo: {
    firstName: 'jay',
    lastName: 'raj',
    age: 10
  }
};

console.log('first name is ', obj.empInfo?.firstName)
// first name is jay

If empInfo doesn’t exist it returns undefined.

Setting Default Using ??

You can also set a default value, in case,obj.empInfo?.firstName returns undefined using Nullish coalescing operator (??)

let obj = {
  keys: [1, 2, 3],
  empInfo: {
    fName: 'jay',
    lastName: 'raj',
    age: 10
  }
};

console.log(`first name ${obj.empInfo?.firstName ?? 'not found'}`)

// "first name not found"