node模块包装为Promise书写法

1. const Promise = require('bluebird')

const fs = Promise.promisifyAll(Promise.promisify(require('fs')))

2.针对node  npm部分模块，比如xml2js，不支持bluebird包装的形式，解决办法

const xml2js = require('xml2js')

const Parser = new xml2js.Parser()

const parseStringAsync = xml => {
return new Promise((resolve, reject) => {
Parser.parseString(xml, (err, result) => {
if (err) {
reject(err)
} else {
resolve(result)
}
})
})
}