async-do-while

A simple library for Bluebird that helps you create while or do-while loops involving asynchronous operations.

One key design goal is maintaining readability. A loop is structured as multiple function calls so that you don't up end with awkwardly indented code.

Usage

A basic do-while loop:

var Async = require('async-do-while');
 
var loop = 0;
Async.do(() => {
    return Promise.delay(25).then(() => {
        loop++;
    });
});
Async.while(() => { return (loop < 10) });
return Async.end();
 

The function passed to do() will be called repeatedly, as long as the function passed to while() returns a truthy value or a promise that resolves to a truthy value. end() is the function that starts the loop. It returns a Bluebird promise. .

To do a while loop (where the continuation condition is checked first), simply flip the order by which do() and while() are called:

var loop = 0;
Async.while(() => { return (loop < 10) });
Async.do(() => {
    return Promise.delay(25).then(() => {
        loop++;
    });
});
return Async.end();

Use return() to return a value (the value that the promise returned by end() fulfills with):

var loop = 0;
Async.while(() => { return (loop < 10) });
Async.do(() => {
    return Promise.delay(25).then(() => {
        loop++;
    });
});
Async.return(() => { return loop });
return Async.end();

If something needs to happen at the beginning of the loop, call begin() with a callback. Typically, you would use this only when you have nested loops.

To break out of a loop, call break(). It throws an exception that is then trapped and ignored by end(). The same Error object is thrown every time. It's exported from the module as AsyncBreak.

var loop = 0;
Async.do(() => {
    return Promise.delay(25).then(() => {
        if (loop === 5) {
            Async.break();
        }
        loop++;
    });
});
Async.while(() => { return (loop < 10) });
return Async.end();