doDuring.js

import noop from 'lodash/noop';
import slice from './internal/slice';
import onlyOnce from './internal/onlyOnce';
import wrapAsync from './internal/wrapAsync';

/**
 * The post-check version of [`during`]{@link module:ControlFlow.during}. To reflect the difference in
 * the order of operations, the arguments `test` and `fn` are switched.
 *
 * Also a version of [`doWhilst`]{@link module:ControlFlow.doWhilst} with asynchronous `test` function.
 * @name doDuring
 * @static
 * @memberOf module:ControlFlow
 * @method
 * @see [async.during]{@link module:ControlFlow.during}
 * @category Control Flow
 * @param {AsyncFunction} fn - An async function which is called each time
 * `test` passes. Invoked with (callback).
 * @param {AsyncFunction} test - asynchronous truth test to perform before each
 * execution of `fn`. Invoked with (...args, callback), where `...args` are the
 * non-error args from the previous callback of `fn`.
 * @param {Function} [callback] - A callback which is called after the test
 * function has failed and repeated execution of `fn` has stopped. `callback`
 * will be passed an error if one occurred, otherwise `null`.
 */
export default function doDuring(fn, test, callback) {
    callback = onlyOnce(callback || noop);
    var _fn = wrapAsync(fn);
    var _test = wrapAsync(test);

    function next(err/*, ...args*/) {
        if (err) return callback(err);
        var args = slice(arguments, 1);
        args.push(check);
        _test.apply(this, args);
    };

    function check(err, truth) {
        if (err) return callback(err);
        if (!truth) return callback(null);
        _fn(next);
    }

    check(null, true);

}