Your question does not really explain what result you are getting and your code looks like it's missing parts of the code. So, all I can really do here to help is to explain generically (using your code where possible) how to solve this class of problem.
If you are ending up with a lot of results that all reference the last value of i in your loop, then you are probably trying to reference i in an async callback but because the callback is called sometime later, the for loop has already finished long before the callback executes. Thus, your value of i is sitting on the last value it would have in the for loop. But, your question doesn't actually show code that does that, so this is just a guess based on the limited result you describe. To solve that type of issue, you have make sure you're separately keeping track of i for each iteration of the loop. There are many ways to do that. In ES6, using let in the for loop definition will solve that entire issue for you. One can also construct a closure, use .forEach(), etc...
Async operations with a loop require extra work and coding to deal with. The modern solution is to convert your async operations to use promises and then use features such as Promise.all() to both tell you when all the async operations are done and to keep the results in order for you.
You can also code it manually without promises. Here's a manual version:
const len = 10;
let text_list = new Array(10);
let doneCnt = 0;
let errFlag = false;
// using let here so each invocation of the loop gets its own value of i
for (let i = 0; i < len; i++) {
tesseract.process("img"+i+".jpg", options, function (err, text) {
if (err) {
console.log("An error occured: ", err);
// make sure err is wrapped in error object
// so you can tell errors in text_list array from values
if (!(err instanceof Error)) {
err = new Error(err);
}
text_list[i] = err;
errFlag = true;
} else {
text_list[i] = text;
}
// see if we're done with all the requests
if (++doneCnt === len) {
if (errFlag) {
// deal with situation where there were some errors
} else {
// put code here to process finished text_list array
}
}
});
}
// you can't process results here because async operations are not
// done yet when code here runs
Or, using promises, you can make a "promisified" version of tesseract.process() and then use promise functionality to track multiple async operations:
// make promisified version of tesseract.process()
tesseract.processP = function(img, options) {
return new Promise(function(resolve, reject) {
tesseract.process(img, options, function(err, text) {
if (err) {
reject(err)
} else {
resolve(text);
}
});
});
}
const len = 10;
let promises = [];
for (let i = 0; i < len; i++) {
promises.push(tesseract.processP("img"+i+".jpg", options));
}
Promise.all(promises).then(function(results) {
// process results array here (in order)
}).catch(function(err) {
// handle error here
});
