Hshen
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compose函数应用

2023年1月5日

预计阅读:1min

koa compose 处理中间件

function compose (middleware) {
  if (!Array.isArray(middleware)) throw new TypeError('Middleware stack must be an array!')
  for (const fn of middleware) {
    if (typeof fn !== 'function') throw new TypeError('Middleware must be composed of functions!')
  }
 
  /**
   * @param {Object} context
   * @return {Promise}
   * @api public
   */
 
  return function (context, next) {
    // last called middleware #
    let index = -1
    return dispatch(0)
    function dispatch (i) {
      if (i <= index) return Promise.reject(new Error('next() called multiple times'))
      index = i
      let fn = middleware[i]
      if (i === middleware.length) fn = next
      if (!fn) return Promise.resolve()
      try {
        return Promise.resolve(fn(context, dispatch.bind(null, i + 1)))
      } catch (err) {
        return Promise.reject(err)
      }
    }
  }
}

redux compose

export default function compose(...funcs: Function[]) {
  if (funcs.length === 0) {
    // infer the argument type so it is usable in inference down the line
    return <T>(arg: T) => arg
  }
 
  if (funcs.length === 1) {
    return funcs[0]
  }
 
  return funcs.reduce(
    (a, b) =>
      (...args: any) =>
        a(b(...args))
  )
}

underscorejs compose