promise_sample.js

'use strict'

const sleep = someFunction => {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve(someFunction())        
        }, 5000)
    })
}

const response = params => {
    return new Promise((resolve, reject) => {
        sleep(() => { resolve(params) })
    })
}

const isValidParams = params => {
    if (!params.id) {
        return false
    }

    return true
}

const searchPriceById = id => {
    return new Promise((resolve, reject) => {
        sleep(() => { resolve(1000) })
    })
}

const getPrice = response({ 'id': 'abc123' })
    .then(params => {
        if (!isValidParams(params)) {
            throw new Error('"id" must be included to params.')
        }

        return searchPriceById(params.id)
    })
    .then(itemPrice => {
        console.log(itemPrice)
    })
    .catch(err => {
        console.log(err)
    })