How to Check if a Value is a Promise in JavaScript ?

To check if a value is a Promise in JavaScript, we can use the instanceof operator. Promises are a specific type of object, and this operator allows you to check if an object is an instance of a particular class or constructor function. so we will use this to check whether the given value is a promise or not.

Example: Here, the isPromise function checks if the provided value is an instance of the Promise constructor. It returns true if it is and false otherwise.

Javascript

function isPromise(value) {
    return value instanceof Promise;
}

// Example usage:
const myPromise = new Promise((resolve, reject) => {
    // Some asynchronous operation
    resolve('Success!');
});

const notAPromise = 'Hello, I am not a Promise!';

console.log(isPromise(myPromise));      // true
console.log(isPromise(notAPromise));    // false

Output

true
false