Example of a simple promise and wrapping subsequent async function calls automatically in a promise

promise_example.js

const makeAPromise = () => {
    return new Promise( (resolve, reject) => {

        const statusCodes = [200, 400]

        // simulation of an async AJAX request
        setTimeout(() => {
            // pick a random status after 3 s
            const status = statusCodes[Math.floor(Math.random() * statusCodes.length)]
            if (status == 200) {
                resolve(status)
            } 
            if (status == 400) {
                reject(status)
            }
        }, 3000)    
    })
}

const myOtherAsyncThing = () => {
    setTimeout(() => { 
        console.log('yay')
    }, 1500)
}

makeAPromise().then(res => console.log(`Your request worked fine and got a ${res} code`))
              .then(myOtherAsyncThing)
              .catch(err => console.error(`Hey, your request crapped out with a ${err} code`))