使用promise 和 generator来管理工作流

根据p219的代码改编

示例代码如下

function oneStep(value){
    return new Promise(function(resolve, reject){
        resolve('one step,' + value);
    })
}

let stepGenerator = function* (){
    try{
        for(let i =0; i < 10; ++i){
            let value = yield oneStep(`step${i}`);
            console.log(`step${i} complete, value:${value}`);
        }
    }catch(e){
        console.log('generator e', e);
    }
}

function run(generator){
    let it = generator();

    function go(result){
        console.log('go,', result);
        if(result.done){
            console.log('done');
            return result.value;
        }

        return result.value.then(function(value){
            console.log('call go again, then');
            return go(it.next(value));
        }).catch(function (error){
            console.log('call go again, catch');
            return go(it.throw(error))
        });
    }
    console.log('call go first');
    return go(it.next());
}

let value = run(stepGenerator);
console.log('value', value);

oneStep代表一个执行步骤，是异步执行的。

stepGenerator代表一个流程，内部包含了一系列的步骤

然后在run函数通过递归的方式执行一个流程，上一步执行完了就执行下一步。

输出结果如下

call go first
go, { value: Promise { 'one step,step0' }, done: false }
value Promise { <pending> }
call go again, then
step0 complete, value:one step,step0
go, { value: Promise { 'one step,step1' }, done: false }
call go again, then
step1 complete, value:one step,step1
go, { value: Promise { 'one step,step2' }, done: false }
call go again, then
step2 complete, value:one step,step2
go, { value: Promise { 'one step,step3' }, done: false }
call go again, then
step3 complete, value:one step,step3
go, { value: Promise { 'one step,step4' }, done: false }
call go again, then
step4 complete, value:one step,step4
go, { value: Promise { 'one step,step5' }, done: false }
call go again, then
step5 complete, value:one step,step5
go, { value: Promise { 'one step,step6' }, done: false }
call go again, then
step6 complete, value:one step,step6
go, { value: Promise { 'one step,step7' }, done: false }
call go again, then
step7 complete, value:one step,step7
go, { value: Promise { 'one step,step8' }, done: false }
call go again, then
step8 complete, value:one step,step8
go, { value: Promise { 'one step,step9' }, done: false }
call go again, then
step9 complete, value:one step,step9
go, { value: undefined, done: true }
done