Async Await Example

async-await-example.js

'use strict';

const students = [
    {
        id: 1,
        name: 'Bart',
    },
    {
        id: 2,
        name: 'Lisa',
    },
    {
        id: 3,
        name: 'Gisborne',
    },
];

const grades = [
    {
        studentId: 1,
        scores: [55, 93, 23],
    },
    {
        studentId: 2,
        scores: [45, 67, 98],
    },
    {
        studentId: 3,
        scores: [32, 76, 28],
    },
];

let getStudentId = (studentName) => {
    return new Promise((resolve, reject) => {
        let result = undefined;

        for (let student of students) {
            if (student.name === studentName) {
                result = student.id;
                break;
            }
        }

        if (result === undefined) {
            reject(null);
        } else {
            resolve(result);
        }
    });
};

let getStudentGrades = (studentId) => {
    return new Promise((resolve, reject) => {
        let result = null;

        for (let grade of grades) {
            if (grade.studentId === studentId) {
                result = grade.scores;
                break;
            }
        }

        if (result === null) {
            reject(null);
        } else {
            resolve(result);
        }
    });
};

let getStudentResult = async (studentName) => {
    let studentId = await getStudentId(studentName);
    let studentScores = await getStudentGrades(studentId);

    let sum = 0;

    for (let score of studentScores)
        sum += score;

    return sum/3;
};

let studentName = 'Bart';
getStudentResult(studentName).then((result) => {
    console.log(`${studentName}'s result is ${result} %.`);
}).catch((error) => {
    console.log(`${studentName} not found!`);
});