CODEWITHSUNDEEP
javascript
Poogy
Poogy

Reputation: 2757

check for undefined key in object - JS

I have this object:

const obj = {
  k1: 1,
  k2: 2
};

which of these 2 methods is the correct one to check if a key doesn't exist, and why?

if (obj.k3 === undefined)

or:

if (typeof obj.k3 === 'undefined')

Is there a better method?

Upvotes: 1

Views: 2275

Answers (2)

Nina Scholz
Nina Scholz

Reputation: 386522

You may consider to use the in operator.

The in operator returns true if the specified property is in the specified object or its prototype chain.

const obj = {
        k1: undefined,
        k2: 2
    };

console.log('k1' in obj);                   //  true
console.log('k3' in obj);                   // false  <--- 

// value check
console.log(obj.k1 === undefined);          //  true
console.log(obj.k3 === undefined);          //  true

// typeof check
console.log(typeof obj.k1 === 'undefined'); //  true
console.log(typeof obj.k3 === 'undefined'); //  true

Upvotes: 1

Taylor Rahul
Taylor Rahul

Reputation: 729

you can use the Object.hasOwnProperty check function which will return or false,

//since k2 exists in your object it will return true, and your if condition will //be executed
if(obj.hasOwnProperty('k2')){
  //perform your action
  //write your code
}

//since k3 does not exists in your object it will return false, and your else //condition will be executed
if(obj.hasOwnProperty('k3')){
}else{
  //perform your action 
  //write your code
}

Upvotes: 0

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