A simple example of Promises in JavaScript

promise.js

console.clear();

function oddOrEven(n)
{
    return new Promise((resolve, reject) => {
        if (typeof(n) != 'number') {
            reject(new TypeError('n must be a number'));
        }
        
        if ((n % 2) == 0) {
            resolve('even');
        }
        
        resolve('odd');
    });
}

oddOrEven(2).then(function (result) {
    console.log('n is ' + result);
}).catch(function (errorObject) {
    console.error(errorObject.message);
});