callback to promise example

.js

const getCourses = () => {
    return new Promise( (resolve, reject) => {
        S3.getObject({
            Bucket: 'your-bucket-here',
            Key: 'your-file.json'
        }, function (err, data){
            if (err !== null){
                reject(err)
            }
            resolve(JSON.parse(data.Body.toString('utf-8')))
        })
    })
}

    getCourses().
    then( data => {
        let message
        let courses = data.data.filter(course => {
            return (course.subject_desc.toLowerCase().includes(CourseType))
        })
        if (!courses.length > 0){
            message = "Sorry, we couldn't find any courses in that discipline or at that level. Let me know if want me to look again for something else."
        } else {
            message = `We found ${courses.length} courses: \n
                ${courses.map(course => `${course.subject} ${course.course_number}-${course.section}: ${course.title}`).join('\n')}
            `
        }
        let response = {
            "dialogAction": {
                "type": "Close",
                "fulfillmentState": "Fulfilled",
                "message": {
                    "contentType": "PlainText",
                    "content": message
                }
            }
        }
        callback(null, response)
    }).catch(err => callback(err))