Node.js async to sync

Question

How can I make this work

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var asyncToSync = syncFunc();  function syncFunc() {     var sync = true;     var data = null;     query(params, function(result){         data = result;         sync = false;     });     while(sync) {}     return data; } 

I tried to get sync function from async one, I need it to use FreeTds async query as sync one

Answer 1

Use deasync - a module written in C++ which exposes Node.js event loop to JavaScript. The module also exposes a sleep function that blocks subsequent code but doesn't block entire thread, nor incur busy wait. You can put the sleep function in your while loop:

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var asyncToSync = syncFunc();  function syncFunc() {     var sync = true;     var data = null;     query(params, function(result){         data = result;         sync = false;     });     while(sync) {require('deasync').sleep(100);}     return data; } 

Answer 2

Nowadays this generator pattern can be a fantastic solution in many situations:

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// nodejs script doing sequential prompts using async readline.question function  var main = (function* () {    // just import and initialize 'readline' in nodejs   var r = require('readline')   var rl = r.createInterface({input: process.stdin, output: process.stdout })    // magic here, the callback is the iterator.next   var answerA = yield rl.question('do you want this? ', res=>main.next(res))        // and again, in a sync fashion   var answerB = yield rl.question('are you sure? ', res=>main.next(res))            // readline boilerplate   rl.close()    console.log(answerA, answerB)  })()    // <-- executed: iterator created from generator main.next()     // kick off the iterator,                  // runs until the first 'yield', including rightmost code                 // and waits until another main.next() happens