Node.js util.types.isPromise() Method

The util.types.isPromise() method is an inbuilt application programming interface of the util module which is primarily designed to support the needs of Node.js own internal APIs. The util.types.isPromise() method is used to determine whether the value is a built-in Promise. 

Syntax:

util.types.isPromise( value )

Parameter: This method accepts a single parameters value that holds any valid JavaScript data types like Boolean, Null, Number, Object, etc. 

Return value: It returns a Boolean value i.e. returns true if the value is a built-in Promise otherwise it returns false. 

The below examples illustrate the use of util.types.isPromise() method in Node.js: 

Example 1:

javascript

// Node.js program to demonstrate the
// util.types.isPromise() method

// Using require to access util module
const util = require('util');

// Using util.types.isPromise() method
console.log(util.types.isPromise(true));

// Using util.types.isPromise() method
console.log(util.types.isPromise(new Set()));

// Using util.types.isPromise() method
console.log(util.types.isPromise(
            new Promise(function (resolve, reject) { })));

Output:

false
false
true

Example 2:

javascript

// Node.js program to demonstrate the
// util.types.isPromise() method

// Using require to access util module
const util = require('util');

// Using util.types.isPromise() method
console.log(util.types.isPromise(true));

// Using util.types.isPromise() method
console.log(util.types.isPromise(new Set()));

// Defining a Promise
const promise = new Promise(function (resolve, reject) {
    const x = "geeksforgeeks";
    const y = "geeksforgeeks"
    if (x === y) {
        resolve();
    } else {
        reject()
    }
});

// Using util.types.isPromise() method
console.log(util.types.isPromise(promise.
    then(function () {
        console.log('Success, You are a GEEK');
    }).
    catch(function () {
        console.log('Some error has occurred');
    })
));

Output:

false
false
true
Success, You are a GEEK

Note: The above program will compile and run by using the node index.js command. 

Reference: https://nodejs.org/dist/latest-v13.x/docs/api/util.html#util_util_types_ispromise_value