Async Await Example

app-promises-problematic.js

const users = [{
  id: 1,
  name: 'Carlo',
  schoolId: 101
},{
  id: 2,
  name: 'Gino',
  schoolId: 123
}];

const grades = [{
  id: 1,
  schoolId: 101,
  grade: 99
}, {
  id: 2,
  schoolId: 123,
  grade: 100
}, {
  id: 3,
  schoolId: 101,
  grade: 90 
}];

const getUser = (id) => {
  return new Promise((resolve, reject) => {
    const user = users.find(user => user.id === id);
    if (user) {
      resolve(user)
    } else {
      reject(`Unable to find user with id of ${id}.`)
    }
  });
};

const getGrades = (schoolId) => {
  return new Promise((resolve) => {
    resolve(grades.filter(grade => grade.schoolId === schoolId))
  })
}

const getStatus = (userId) => {
  let user;
  return getUser(userId)
    .then(tempUser => {
      user = tempUser;
      return getGrades(user.schoolId)
    })
    .then(grades => {
      let average = 0;

      if (grades.length > 0) {
        average = grades.map(grade => grade.grade).reduce((a, b) => a + b) / grades.length;
      }

      return `${user.name} has a ${average}% in the class.`
    })
}

getStatus(1)
  .then((status) => {
    console.log(status)
  })
  .catch(err => {
    console.log(err)
  })

getGrades(123)
  .then(res => {
    console.log(res)
  })

getUser(2)
  .then(res => {
    console.log(res)
  })
  .catch(err => {
    console.log(err)
  })

app-promises.js

const users = [{
  id: 1,
  name: 'Carlo',
  schoolId: 101
},{
  id: 2,
  name: 'Gino',
  schoolId: 123
}];

const grades = [{
  id: 1,
  schoolId: 101,
  grade: 99
}, {
  id: 2,
  schoolId: 123,
  grade: 100
}, {
  id: 3,
  schoolId: 101,
  grade: 90 
}];

const getUser = (id) => {
  return new Promise((resolve, reject) => {
    const user = users.find(user => user.id === id);
    if (user) {
      resolve(user)
    } else {
      reject(`Unable to find user with id of ${id}.`)
    }
  });
};

const getGrades = (schoolId) => {
  return new Promise((resolve) => {
    resolve(grades.filter(grade => grade.schoolId === schoolId))
  })
}

const getStatus = async (userId) => {
  const user = await getUser(userId);
  const grades = await getGrades(user.schoolId);
  let average = 0;

  if (grades.length > 0) {
    average = grades.map(grade => grade.grade).reduce((a, b) => a + b) / grades.length;
  }

  return `${user.name} has a ${average}% in the class.`
}

getStatus(1)
  .then(name => console.log(name))
  .catch(err => console.log(err))
  

currency-convert.js

const axios = require('axios');

process.env.NODE_TLS_REJECT_UNAUTHORIZED = "0";

const getExchangeRate = async (from, to) => {
  try {
    const response = await axios.get('http://data.fixer.io/api/latest?access_key=955d2cec3e9fc16b4d5460de8a9be7ca')
    const euro = 1 / response.data.rates[from];
    const rate = euro * response.data.rates[to];

    if (isNaN(rate)) {
      throw new Error()
    }

    return rate
  } catch (error) {
    throw new Error(`Unable to get exchange rate for ${from} adn ${to}`);    
  }
};


const getCountries = async (currencyCode) => {
  try {
    const response = await axios.get(`https://restcountries.eu/rest/v2/currency/${currencyCode}`);
    return response.data.map(country => country.name);
  } catch (error) {
    throw new Error(`Unable to get countries that use ${currencyCode}`); 
  }
}

const convertCurrency = async (from, to, amount) => {
  const rate = await getExchangeRate(from, to)
  const countries = await getCountries(to);
  const convertedAmount = (rate * amount).toFixed(2)

  return `${amount} ${from} is worth ${convertedAmount} ${to}. You can spend these in the following countries: ${countries.join(', ')}.`;
}

convertCurrency('USD', 'PHP', 20)
  .then(res => {
    console.log(res)
  })
  .catch(e => {
    console.log(e.message)
  });