Here are different ways to check a key exists in an object in JavaScript.

Note: Objects in JavaScript are non-primitive data types that hold an unordered collection of key-value pairs.

1. Using in Operator

The in operator in JavaScript checks if a key exists in an object by returning a boolean value. It verifies if the specified property is present within the object, simplifying key existence validation.

Syntax

'key' in object

let exampleObj = {
    id: 1,
    remarks: 'Good'
}

// Check for the keys
let output1 = 'name' in exampleObj;
let output2 = 'remarks' in exampleObj;

console.log(output1);
console.log(output2);

let exampleObj = {

    id: 1,

    remarks: 'Good'

}

​

// Check for the keys

let output1 = 'name' in exampleObj;

let output2 = 'remarks' in exampleObj;

​

console.log(output1);

console.log(output2);

false
true

2. Using hasOwnProperty() Method

The hasOwnProperty() method returns a boolean value that indicates whether the object has the specified property. The required key name could be passed in this function to check if it exists in the object. 

Syntax

object.hasOwnProperty('key') 

let exampleObj = {
    id: 1,
    remarks: 'Good'
}

// Check for the keys
let output1 = exampleObj.hasOwnProperty('name');
let output2 = exampleObj.hasOwnProperty('remarks');
console.log(output1);
console.log(output2);

let exampleObj = {

    id: 1,

    remarks: 'Good'

}

​

// Check for the keys

let output1 = exampleObj.hasOwnProperty('name');

let output2 = exampleObj.hasOwnProperty('remarks');

console.log(output1);

console.log(output2);

false
true

3. Using the Object.keys() Method

The Object.keys() method in JavaScript retrieves an array of the object's keys. By checking if the desired key is included in this array, one can determine if it exists in the object.

Syntax

Object.keys(obj);

const obj = {
name: 'Sandeep',
age: '32'
};

if (Object.keys(obj).includes('age')) {
    console.log('true');
} else {
    console.log('false');
}

const obj = {

name: 'Sandeep',

age: '32'

};

​

if (Object.keys(obj).includes('age')) {

    console.log('true');

} else {

    console.log('false');

}

true