javascript 将承诺添加到 for 循环中的承诺数组
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adding promises to an array of promises in a for loop
提问by redshark1802
let's assume the following example:
让我们假设以下示例：
var bb = require('bluebird');
var promiseStack = [];
var deferred = bb.defer();
promiseStack.push(deferred.promise);
bb.delay(2500).then(function() {
deferred.resolve();
});
bb.all(promiseStack).then(function() {
console.log('done');
});
Why isn't it possible to do the following:
为什么不能执行以下操作：
var bb = require('bluebird');
var promiseStack = [];
for(var i = 1; i < 10; i++) {
var deferred = bb.defer();
promiseStack.push(deferred.promise);
bb.delay(2500).then(function() {
deferred.resolve();
});
}
bb.all(promiseStack).then(function() {
console.log('done');
});
It takes aprox. 2500ms but console.log('done')isn't called.
What's the problem with, am I doing wrong?
它需要大约。2500 毫秒，但console.log('done')没有被调用。有什么问题，我做错了吗？
The best, redshark1802
最好的，redshark1802
回答by Bergi
What's the problem with, am I doing wrong?
有什么问题，我做错了吗？
Your deferredvariable is not local to the loop body, but on a global scope. You're overwriting it each time with a new Deferred, and resolving only the last of them (but multiple times).
您的deferred变量不是循环体的局部变量，而是在全局范围内。你每次都用一个新的 Deferred 覆盖它，并且只解决最后一个（但多次）。
To fix it, you could try a closure, but you shouldn't use Deferredanyway. Just use the promise you already have!
要修复它，您可以尝试使用closure，但无论如何都不应该使用Deferred。只需使用您已有的承诺！
var bb = require('bluebird');
var promiseStack = [];
for(var i = 1; i < 10; i++) // 1 to 9 ???
promiseStack.push( bb.delay(2500) );
bb.all(promiseStack).then(function() {
console.log('done');
});
