I have a bit of trouble getting into this whole async stuff. I'm using pdf.js to read the contents of a pdf file. Everything is working, however the execution order is causing me troubles. This is the code I have:
function getText(data) {
var contents = [];
PDFJS.getDocument(data).then(function(pdf) {
var numPages = pdf.pdfInfo.numPages;
for (var i = 1; i <= numPages; i++) {
pdf.getPage(i).then(function(page) {
page.getTextContent().then(function(content) {
contents.concat(content.bidiTexts);
})
});
}
})
}
This is working as intended, however, I would like to pass contents
when all pages are processed and their bidiTexts are concated to contents. If I just put a function call with contents
as argument before the last closing }
then it gets called to early.
Try using promises:
function getText(data) {
var contents = [];
var promises = [];
PDFJS.getDocument(data).then(function(pdf) {
var numPages = pdf.pdfInfo.numPages;
for (var i = 1; i <= numPages; i++) {
var deferred = $.Deferred(); //Create a deferred object
promises.push(deferred.promise()); //push promise to the list
pdf.getPage(i).then(function(page) {
page.getTextContent().then(function(content) {
contents.concat(content.bidiTexts);
deferred.resolve(); //resolve the deferred object
})
});
}
$.when.apply($,promises).then(function(){ //callback executed when all deferreds are resolved
//do your task with contents
});
})
}
This is just a demo how to use promises. In real applications, you have to take care of errors by using deferred.reject
and handle it in the second callback to $.when