koa中的洋葱圈模型核心代码
npm地址：www.npmjs.com/package/koa…
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)
}
}
}
}
用法测试
function wait (ms) {
return new Promise((resolve) => setTimeout(resolve, ms || 1))
}
const stack = []
stack.push(async (context, next) => {
context.arr.push(1)
console.log('log=>1-start',context.arr);
await wait(1)
try{
await next()
}
catch(e){
console.log('log=>e',e);
}
await wait(1)
context.arr.push(6)
console.log('log=>1-end',context.arr);
})
stack.push(async (context, next) => {
context.arr.push(2)
await wait(1)
console.log('log=>2-start',context.arr);
// throw new Error()
await next()
await wait(1)
context.arr.push(5)
console.log('log=>2-end',context.arr);
})
stack.push(async (context, next) => {
context.arr.push(3)
await wait(1)
console.log('log=>3-start',context.arr);
await next()
await wait(1)
context.arr.push(4)
console.log('log=>3-end',context.arr);
})
const fn = compose(stack)
// const fn1 = compose1(stack)
const ctx1 = { arr: [] }
fn(ctx1,async function (){
console.log('到洋葱芯了')
await wait(1000)
})
.then(()=>{
console.log('log-完事了=>ctx1.arr',ctx1.arr);
})
