从蓝森林与JSON构建承诺

Question

我有一个uniq问题。我有JSON数据，代表生成承诺的步骤。

[ 
    { 
    action: 'wait' 
    }, 
    { 
    action: 'screenshot' 
    } 
] 

现在我正在用Bluebird产生这个承诺。

var pr = require('bluebird/js/main/promise')(); 
var R = require('bluebird'); 

var Worker = { 
    open: function() { 
    return new pr(function (resolve, reject) { 
     resolve('opened'); 
    }); 
    }, 
    wait: function (milliseconds) { 
    return pr.delay(milliseconds); 
    }, 

    screenshot: function (milliseconds) { 
    return new pr(function (resolve, reject) { 
     resolve('take screenshot'); 
    }); 
    } 
} 

var defers = []; 
Worker.open(); 
JSON.forEach(function (vl) { 
    var defer = R.defer(); 
    defers.push(defer.promise); 
    Worker[vl.action]().then(function() { 
    // do something 
    defer.resolve(); 
    }); 
}); 
R.all(defers).then(function() { console.log('finished');}); 

现在，这是不行的，因为承诺没有链接。我被建议我把它们连起来。

var pr = require('bluebird/js/main/promise')(); 
var R = require('bluebird'); 

var Worker = { 
    open: function() { 
    return new pr(function (resolve, reject) { 
     resolve('opened'); 
    }); 
    }, 
    wait: function (milliseconds) { 
    return pr.delay(milliseconds); 
    }, 

    screenshot: function (milliseconds) { 
    return new pr(function (resolve, reject) { 
     resolve('take screenshot'); 
    }); 
    } 
} 

var defers = []; 
var chain = Worker.open(); 
JSON.forEach(function (vl) { 
    var defer = R.defer(); 
    defers.push(defer.promise); 
    chain = chain[vl.action]().then(function() { 
    // do something 
    defer.resolve(); 
    }); 
}); 
R.all(defers).then(function() { console.log('finished')}); 

但是，这也不能正常工作，就如何从JSON数据的承诺基于函数有什么建议？

Answer 1

你想采取行动的阵列，并减少到一个单一的承诺值。

const actions = [ 
    {action: 'wait'}, 
    {action: 'screenshot'} 
]; 

const allDone = actions.reduce((promise, item) => 
    promise.then(Worker[item.action]), Promise.resolve()); 

allDone.then(() => console.log("All done!")); 

这为读取：“通过与.then()链项目的行动上的承诺，从空洞的承诺开始减少阵列”

---

每请求，与ES5（了解ES2015，它的真棒！）

var actions = [ 
    {action: 'wait'}, 
    {action: 'screenshot'} 
]; 

var allDone = actions.reduce(function(promise, item) { 
    return promise.then(Worker[item.action]) 
}, Promise.resolve()); 

allDone.then(function() { 
    console.log("All done!"); 
}); 

Answer 2

我想你对链接承诺有点困惑。

您需要执行上一个操作承诺的.then(...)中的下一个操作。

var chain = Worker.open(); 
JSON.forEach(function (vl) { 
    chain = chain.then(function() { 
     //You need to return to promise from Worker[vl.action]() to correctly chain actions 
     return Worker[vl.action](); 
    }); 
    //"chain" is now synchronized with the promise of the last chained action 
});