Node.js Nodejs/Q:按顺序链接承诺
我想做一些非常简单的事情,但我一点都不懂Node.js Nodejs/Q:按顺序链接承诺,node.js,promise,sequence,q,chain,Node.js,Promise,Sequence,Q,Chain,我想做一些非常简单的事情,但我一点都不懂 var Q = require('q'); var funcs = ["first", "second", "third", "fourth"]; function main(){ // really don't know how to chain sequentially here ... var result = Q(); funcs.forEach(function (f) { result = treat(
var Q = require('q');
var funcs = ["first", "second", "third", "fourth"];
function main(){
// really don't know how to chain sequentially here ...
var result = Q();
funcs.forEach(function (f) {
result = treat(f).then(f);
});
}
function treat(t){
var deferred = Q.defer();
setTimeout(function(){
deferred.resolve("treated "+ t);
},2000);
return deferred.promise;
}
main();
我希望按顺序“处理”funcs数组的每个元素,然后输出如下:
treated first
//2 seconds later
treated second
//2 seconds later
treated third
//2 seconds later
treated fourth
我没法做到:(应该很简单,我没听懂什么:(从你的例子来看,我假设你已经看到了,但没有理解它 原始示例使用“瀑布”模型,当每个函数的输出作为输入传递给下一个函数时:
var funcs = [foo, bar, baz, qux];
var result = Q(initialVal);
funcs.forEach(function (f) {
result = result.then(f);
});
return result;
但您只想按顺序执行所有函数,因此您可以简单地将每个函数与其变量绑定:
var args = ["first", "second", "third", "fourth"];
var result = Q();
args.forEach(function (t) {
result = result.then(treat.bind(null, t));
});
return result;
在我的示例中,treat
函数将按顺序调用4次,result
promise将使用最新的treat
call值进行解析(之前所有调用的结果将被忽略)
诀窍是。然后方法接受一个处理程序,该处理程序将在解析当前承诺后调用,并返回一个新承诺。因此,您应该传递到。然后一个函数,该函数应该在执行链的下一步调用。treat.bind(null,t)
将treat
函数与属性t
绑定。换句话说,它返回一个新函数,该函数将调用treat
,并将t
作为其第一个参数传递