面试题1

bus.js

const listeners = {}

// 不是很理解第三条。。。

const bus = {
  on(event, fun) {
    let handler
    let before
    if (typeof fun === 'object' && fun.fn) {
      handler = fun.fn
      before = fun.before
    } else {
      handler = fun
    }

    let realHandler
    const promise = new Promise((resolve, reject) => {
      realHandler = (...args) => {
        // 如何确定`handler`是否执行完？
        handler(...args)
      }
    })

    before = Array.isArray(before) ? before : [before]
    if (listeners[event]) {
      if (before) {
        let index = -1
        let i
        for (let i = 0; i<before.length; i++) {
          i = listeners[event].indexOf(before(i))
          if (i > index) {
            index = i
          }
        }
        if (index === -1) {
          // throw error?
        }
        listeners[event].splice(index, 0, realHandler)
      } else {
        listeners[event].push(realHandler)
      }
    }
    return promise
  },
  trigger(event, ...args) {
    const eListeners = listeners[event]
    // 检查
    eListeners.forEach((listener) => listener(...args))
  },
}

gql.js

function parse(str) {
  let type
  let fields
  let attrs
  let relations = []
  let typeSplit = str.split('{')
  let typeWithAttrs = typeSplit[0]

  // type and attrs
  if (typeWithAttrs.indexOf('(') !== -1) {
    let typeAttrSplit = typeWithAttrs.split('(')
    type = typeAttrSplit[0]
    attrs = typeAttrSplit[1].substr(0, typeAttrSplit[1] - 2) // 去掉后面的)
    arrts = attrs.split(',')
    attrs = attrs.reduce((result, attr) => {
      let [key, value] = attr.split(':')
      result[key] = value
    }, {})
  } else {
    type = typeWithAttrs
  }

  fields = typeSplit[1].substr(0, typeSplit[1].length - 2) // 去掉}
  // 这里还要处理`relation`里面的`,`
  fields = fields.split(',')

  fields = fields.reduce((result, field) => {
    if (field.indexOf('{') === -1) {
      result.push(field)
    } else {
      relations.push(field)
    }
  }, [])

  return {
    type,
    fields,
    attrs,
  }
}