可以承诺用于触发一堆异步加载吗？

I'm having problmes in finding the use of promises and also admit that my understanding of them is very basic. From what I can tell, they just seem to mimic sync behavior.

我在寻找承诺的使用方面遇到了问题，并承认我对它们的理解是非常基础的。据我所知，他们似乎只是模仿同步行为。

Is it possible to use promises and keep the async behaviour then use then() once they have all completed?

是否有可能使用promises并保持异步行为然后在完成后使用then（）？

Such as this...

比如这......

var fileRegister = [ 'fileA', 'fileB', 'fileC' ];

for( i in fileRegister ) {
  asyncLoadFile( fileRegister[ i ], function( err, data ) {
    delete fileRegister[ i ];
    if ( ! fileRegister.length ) {
      console.log('done');
    }
  });
}

2 个解决方案

#1

Yes, you can use Promise.all to wait on multiple promises:

是的，您可以使用Promise.all等待多个承诺：

var fileRegister = [ 'fileA', 'fileB', 'fileC' ];

// returns a promise for a file
function loadFile(filename) {
    return new Promise(function (resolve, reject) {
        asyncLoadFile(filename, function (err, data) {
            if (err) {
                reject(err);
            }
            resolve(data);
        });
    });
}

Promise.all(fileRegister.map(loadFile))
    .then(function (files) {
        console.log("done");
    });

#2

I'm truly surpised there seems to be no authoratative answer for this on the site. Yes, you can create a bunch of promises (each wrapping an async operation) and then call Promise,all which will resolve once they all do:

我真的很惊讶，在网站上似乎没有任何authoratative答案。是的，你可以创建一堆promises（每个包装一个异步操作），然后调用Promise，所有这些都会解决它们：

var p1 = new Promise(function(resolve, reject) { 
  setTimeout(resolve, 1000, "one"); 
}); 
var p2 = new Promise(function(resolve, reject) { 
  setTimeout(resolve, 2000, "two"); 
});
var p3 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 3000, "three");
});
var p4 = new Promise(function(resolve, reject) {
  setTimeout(resolve, 4000, "four");
});
var p5 = new Promise(function(resolve, reject) {
  reject("reject");
});

Promise.all([p1, p2, p3, p4, p5]).then(function(value) { 
  console.log(value);
}, function(reason) {
  console.log(reason)
});

This is part of the E^ specification and is supported by most implementations.

这是E ^规范的一部分，并得到大多数实现的支持。

#1