2020.9.28 Generator 自动执行

[SampsonKY]

基于 thunk 的自动执行

function thunk(fn){
    return (...args)=>{
        return (callback)=>{
            fn.call(this, ...args, callback)
        }
    }
}

function run(gen){
    let g = gen()
    
    function next(err, data){
        let ret = g.next(data)
        if(ret.done) return ret.value
        ret.value(next)
    }
    next()
}

// 示例
const fs = require('fs')
let readFileThunk = thunk(fs.readFile)

function *gen(){
    let r1 = yield readFileThunk('fileA')
    console.log(r1.toString())
    let r2 = yield readFileThunk('fileB')
    console.log(r2.toString())
}
run(gen)

基于 Promise 的自动执行

function promisify(fn){
    return (...args)=>{
        return new Promise((resolve, reject)=>{
            fn(...args, function(err, data){
                if(err) return reject(err)
                resolve(data)
            })
        })
    }
}

function run(gen){
    let g = gen()
    
    function next(data){
        let ret = g.next(data)
        if(ret.done) return ret.value
        ret.value.then((data)=>{
            next(data)
        })
    }
}

//示例
let readFile = promisify(fs.readFile)
function *gen(){
    let r1 = yield readFile('fileA')
    console.log(r1.toString())
    let r2 = yield readFile('fileB')
    console.log(r2.toString())
}
run(gen)

co 模块

function co(gen){
    var ctx = this

    return new Promise(function(resolve, reject){
        if(typeof gen === 'function') gen = gen.call(ctx)
        if(!gen || typeof gen.next !== 'function') return resolve(gen)

        onFulfilled()
        function onFulfilled(res){
            var ret
            try {
                ret = gen.next(res)
            } catch (e) {
                return reject(e)
            }
            next(ret)
        }

        function onRejected(err){
            var ret
            try {
                ret = gen.throw(err)
            } catch (e) {
                return reject(e)
            }
            next(ret)
        }

        function next(ret){
            if (ret.done) return resolve(ret.value);
            var value = toPromise.call(ctx, ret.value);
            //var value = ret.value
            if (value && isPromise(value)) return value.then(onFulfilled, onRejected);
            return onRejected(
              new TypeError(
                'You may only yield a function, promise, generator, array, or object, '
                + 'but the following object was passed: "'
                + String(ret.value)
                + '"'
              )
            );
        } 
    })
}

function isPromise(obj){
    return 'function' == typeof obj.then
}