JQuery 中的多个承诺解析

Question

我有这个多重承诺请求，需要在继续下一组请求之前解决。

如果 printItemList 长度为 1，则工作正常。但是当它超过 2 时，问题就开始出现。

这个想法是在成功解决前一个print_label后触发print_label。现在它立即被解雇，而不是等待以前的请求完成。

我在这里做错了什么。

对此的任何帮助将不胜感激。

function print_batch(printItemList){
var chain = $.when();
var arr = [];
for(var batch_size = 0; batch_size < printItemList.length; batch_size ++){
(function(i){
chain = chain.then(function() {
$.when.apply($, arr).done(function(){
arr = print_label(printItemList[i]);
});
});
})(batch_size);
}
}
function print_label(selectedRow) {
var d = $.Deferred();
var chain = $.when();
var arr = [];
var request = buildLabel(selectedRow);
var noOfLabel = parseInt(selectedRow.labelCount);
var url = 'API_URL';
var epos = new epson.ePOSPrint(url);
for (var count = 0; count < noOfLabel; count++) {
(function(i){
chain = chain.then(function() {
var def = sendRequest(selectedRow, epos, request);
arr.push(def);
return def;
});
})(count);
}
return arr;
}
function sendRequest(selectedRow, epos, request){
var deferred = $.Deferred();
epos.send(request);
epos.onreceive = function(res) {
return deferred.resolve(res);
}
epos.onerror = function(err) {
return deferred.reject();
}
return deferred.promise();
}

Answer 1

function print_batch(printItemList){
//create recursive method
function print_next_label(index) {
//if we have not reached the end of the list, do more work
if (index < printItemList.length) {
//call the method, wait for all the promises to finish
$.when.apply($, print_label(printItemList[index])).done(function(){
//now that they are done, try to print the next label
print_next_label(++index);
});
}
}

//start the recursive method loop with index 0
print_next_label(0);
}