While loop with promises

by

Here’s a reusable function that I think is pretty clear.

var Q = require("q");

// `condition` is a function that returns a boolean
// `body` is a function that returns a promise
// returns a promise for the completion of the loop
function promiseWhile(condition, body) {
    var done = Q.defer();

    function loop() {
        // When the result of calling `condition` is no longer true, we are
        // done.
        if (!condition()) return done.resolve();
        // Use `when`, in case `body` does not return a promise.
        // When it completes loop again otherwise, if it fails, reject the
        // done promise
        Q.when(body(), loop, done.reject);
    }

    // Start running the loop in the next tick so that this function is
    // completely async. It would be unexpected if `body` was called
    // synchronously the first time.
    Q.nextTick(loop);

    // The promise
    return done.promise;
}


// Usage
var index = 1;
promiseWhile(function () { return index <= 11; }, function () {
    console.log(index);
    index++;
    return Q.delay(500); // arbitrary async
}).then(function () {
    console.log("done");
}).done();

More Related Contents:

  1. How to chain a variable number of promises in Q, in order?
  2. Issue in returning data retrieved from DB queries called in the loop
  3. if-else flow in promise (bluebird)
  4. How do I properly test promises with mocha and chai?
  5. Timeout in async/await
  6. return value after a promise [duplicate]
  7. Why is ‘this’ undefined inside class method when using promises? [duplicate]
  8. How to find which promises are unhandled in Node.js UnhandledPromiseRejectionWarning?
  9. nodejs – How to promisify http.request? reject got called two times
  10. Are there still reasons to use promise libraries like Q or BlueBird now that we have ES6 promises? [closed]
  11. Using Promises with fs.readFile in a loop
  12. Proper way to skip a then function in Q Promises
  13. async await with setInterval
  14. What happens if i reject / resolve multiple times in Kriskowal’s q?
  15. Node.js Event loop
  16. How do I handle exceptions globally with native promises in node.js?
  17. Return value in function from a promise block
  18. javascript promise not passing all arguments (using Q)
  19. How to wait for a stream to finish piping? (Nodejs)
  20. Node.js – Using the async lib – async.foreach with object
  21. Node.js promise request return
  22. req.body empty on posts
  23. Get ‘spawn cmd ENOENT’ when try to build Cordova application (event.js:85)
  24. What exactly does “/usr/bin/env node” do at the beginning of node files?
  25. npm install error – unable to get local issuer certificate
  26. Install Node.js on Ubuntu
  27. NPM doesn’t install any modules: network socket hangs up
  28. bcrypt invalid elf header when running node app
  29. How do I fix a vulnerable npm package in my package-lock.json that isn’t listed in the package.json?
  30. How to get SCSS variables into react

Leave a Comment