Nodejs循环使用回调函数

Question

I am new to nodejs callback function. I have to find phones list between two price ranges given, if there are no 15 phones in the obtained list , I have to change the price range until I got 15 phones. Actually I wrote function for searching phones from database in another file, from that file I send callback to calling function. After I got callback I have to check the array size if array size is less than 15 then change the price range and have to call the same function like Recursion or looping. I am unable to handle the callback function. Please help me to write the correct code.

 while(true ){
            console.log("around came")
             Search.findBestMobile(context.end_price , context.start_price , function(data){
                 console.log("Best Mobile");
                 size = data.hits.hits.length;
                 if(size >= 15){
                     context.phone_list = makeStringFromArray(data.hits.hits);
                     cb(context);
                     break;
                 }else{
                     context.start_price += 1000;
                     context.end_price   += 1000;
                 }
             });
         }

But in above code, break is unreachable statement. I can't handle it. please help me.

Answer 1

The problem is that you are trying to use asynchronous code in synchronous way. That simply won't do, because callback can be called seconds later. Beside that break won't work if called inside function. What are you really doing is calling Search.findBestMobile infinite number of times. Node.js has only single thread that it uses to run your code and you are blocking it. So callbacks won't be called.

What you need to do is to use recursion or other async approach to loops. One simple way of doing it would be to call your outer function again with new context.

function searchRange(context, cb) {
    Search.findBestMobile(context.end_price , context.start_price , function(data){
                 console.log("Best Mobile");
                 size = data.hits.hits.length;
                 if(size >= 15){
                     context.phone_list = makeStringFromArray(data.hits.hits);
                     cb(context);
                 }else{
                     context.start_price += 1000;
                     context.end_price   += 1000;
                     searchRange(context, cb);
                 }
             });
}